diff --git a/.env.example b/.env.example
index fbd32428..882a6dc8 100644
--- a/.env.example
+++ b/.env.example
@@ -69,12 +69,26 @@ DEBUG_DB=false
 # Log http requests
 LOG_HTTP=false
 
-# MCP server (community): service account the embedded MCP uses to talk to this Docmost instance
+# MCP server (community): the embedded /mcp endpoint authenticates PER USER.
+# An MCP client authenticates with one of:
+#   - HTTP Basic: `Authorization: Basic base64(email:password)` — the user's own
+#     Docmost login/password. The server validates the credentials and the MCP
+#     session then acts under that user's permissions (edits attributed to them).
+#   - Bearer access JWT: `Authorization: Bearer <access-jwt>` (the user's
+#     `authToken` cookie value). Validated as an ACCESS token.
+#
+# OPTIONAL service-account fallback. When a request carries NEITHER Basic NOR
+# Bearer credentials and these are set, the MCP session falls back to this
+# shared service account (back-compat; useful for CI/scripts). Leave BLANK to
+# require per-user credentials.
 MCP_DOCMOST_EMAIL=
 MCP_DOCMOST_PASSWORD=
 # MCP_DOCMOST_API_URL=http://127.0.0.1:3000/api
-# Optional bearer token to protect the /mcp endpoint. If unset, /mcp relies on
-# the workspace MCP toggle and network isolation (do not expose the port publicly).
+# Optional shared guard for the /mcp endpoint. When set, every /mcp request must
+# carry a matching `X-MCP-Token` header (separate from `Authorization`, which now
+# carries the per-user credentials). When unset, /mcp relies on the per-user
+# credentials above plus the workspace MCP toggle and network isolation (do not
+# expose the port publicly).
 # MCP_TOKEN=
 # MCP_SESSION_IDLE_MS=1800000
 
diff --git a/apps/server/src/core/auth/auth.module.ts b/apps/server/src/core/auth/auth.module.ts
index c440bdc2..236f4dd5 100644
--- a/apps/server/src/core/auth/auth.module.ts
+++ b/apps/server/src/core/auth/auth.module.ts
@@ -10,6 +10,6 @@ import { TokenModule } from './token.module';
   imports: [TokenModule, WorkspaceModule],
   controllers: [AuthController],
   providers: [AuthService, SignupService, JwtStrategy],
-  exports: [SignupService],
+  exports: [SignupService, AuthService],
 })
 export class AuthModule {}
diff --git a/apps/server/src/core/auth/services/auth.service.ts b/apps/server/src/core/auth/services/auth.service.ts
index bfd8e1a0..def3155c 100644
--- a/apps/server/src/core/auth/services/auth.service.ts
+++ b/apps/server/src/core/auth/services/auth.service.ts
@@ -57,7 +57,23 @@ export class AuthService {
     @Inject(AUDIT_SERVICE) private readonly auditService: IAuditService,
   ) {}
 
-  async login(loginDto: LoginDto, workspaceId: string) {
+  /**
+   * Verify a user's email + password WITHOUT any side effects: it performs the
+   * exact same user lookup, password comparison, email-verified and disabled
+   * checks as `login()`, but does NOT mint a session/token, does NOT write the
+   * USER_LOGIN audit event, and does NOT update lastLoginAt. Returns the matched
+   * user on success; throws UnauthorizedException (credentials) or whatever
+   * `throwIfEmailNotVerified` throws otherwise.
+   *
+   * Use this for repeated per-request credential re-validation (e.g. the /mcp
+   * anti-fixation check on subsequent requests) where minting a new DB session
+   * and audit row on every call would be audit spam / a session-table DoS. The
+   * full `login()` reuses it so there is no behaviour drift between the two.
+   */
+  async verifyUserCredentials(
+    loginDto: LoginDto,
+    workspaceId: string,
+  ): Promise<User> {
     const user = await this.userRepo.findByEmail(loginDto.email, workspaceId, {
       includePassword: true,
     });
@@ -84,6 +100,12 @@ export class AuthService {
       appSecret: this.environmentService.getAppSecret(),
     });
 
+    return user;
+  }
+
+  async login(loginDto: LoginDto, workspaceId: string) {
+    const user = await this.verifyUserCredentials(loginDto, workspaceId);
+
     user.lastLoginAt = new Date();
     await this.userRepo.updateLastLogin(user.id, workspaceId);
 
diff --git a/apps/server/src/integrations/mcp/mcp-auth.helpers.ts b/apps/server/src/integrations/mcp/mcp-auth.helpers.ts
new file mode 100644
index 00000000..6eb17ab0
--- /dev/null
+++ b/apps/server/src/integrations/mcp/mcp-auth.helpers.ts
@@ -0,0 +1,379 @@
+// Pure, self-contained helpers for the embedded /mcp per-user auth flow. They
+// are deliberately framework-free (no Nest, no DI, no concrete service imports)
+// so they can be unit-tested in isolation WITHOUT loading the heavy auth/space
+// dependency graph, and reused by McpService. Nothing here logs the password or
+// the Authorization header.
+import { UnauthorizedException } from '@nestjs/common';
+import { JwtType } from '../../core/auth/dto/jwt-payload';
+
+/**
+ * Decode an `Authorization: Basic base64(email:password)` header into its
+ * email/password parts. The split is on the FIRST ':' because a password may
+ * itself contain ':' characters (everything after the first ':' is the
+ * password). Returns null when the header is absent or not a Basic header, or
+ * when no ':' separator is present (malformed credentials).
+ */
+export function parseBasicAuth(
+  authHeader: string | undefined,
+): { email: string; password: string } | null {
+  if (!authHeader || !authHeader.startsWith('Basic ')) return null;
+  const b64 = authHeader.slice('Basic '.length).trim();
+  let decoded: string;
+  try {
+    decoded = Buffer.from(b64, 'base64').toString('utf8');
+  } catch {
+    return null;
+  }
+  const sep = decoded.indexOf(':');
+  if (sep === -1) return null; // no separator -> not valid email:password
+  const email = decoded.slice(0, sep);
+  if (!email) return null; // empty email -> not valid credentials
+  return {
+    email,
+    password: decoded.slice(sep + 1),
+  };
+}
+
+/**
+ * Lightweight in-memory, per-key fixed-window rate limiter for FAILED /mcp
+ * Basic logins. Calling AuthService.login directly bypasses the controller's
+ * ThrottlerGuard, so this blunts brute-force attempts against /mcp. State lives
+ * in-process (per server instance); it is intentionally simple and not shared
+ * across a cluster — it is a speed bump, not a hard security boundary.
+ *
+ * A key is typically `<ip>` and/or `<ip>:<email>`. When the number of failures
+ * within `windowMs` reaches `threshold`, `isBlocked` returns true until the
+ * window rolls over. A SUCCESSFUL login should clear the key via `reset`.
+ */
+export class FailedLoginLimiter {
+  private readonly windowMs: number;
+  private readonly threshold: number;
+  // key -> { count, windowStart }
+  private readonly buckets = new Map<
+    string,
+    { count: number; windowStart: number }
+  >();
+
+  constructor(threshold = 5, windowMs = 60_000) {
+    this.threshold = threshold;
+    this.windowMs = windowMs;
+  }
+
+  private bucket(key: string, now: number) {
+    const existing = this.buckets.get(key);
+    if (!existing || now - existing.windowStart >= this.windowMs) {
+      const fresh = { count: 0, windowStart: now };
+      this.buckets.set(key, fresh);
+      return fresh;
+    }
+    return existing;
+  }
+
+  /** True when the key has already reached the failure threshold this window. */
+  isBlocked(key: string, now: number = Date.now()): boolean {
+    const b = this.bucket(key, now);
+    return b.count >= this.threshold;
+  }
+
+  /** Record one failed attempt for the key (within the current window). */
+  recordFailure(key: string, now: number = Date.now()): void {
+    const b = this.bucket(key, now);
+    b.count += 1;
+  }
+
+  /** Clear the key after a successful login so it does not accumulate. */
+  reset(key: string): void {
+    this.buckets.delete(key);
+  }
+
+  /** Drop expired buckets to bound memory. Safe to call periodically. */
+  sweep(now: number = Date.now()): void {
+    for (const [key, b] of this.buckets) {
+      if (now - b.windowStart >= this.windowMs) this.buckets.delete(key);
+    }
+  }
+}
+
+// The per-session DocmostMcpConfig shape understood by @docmost/mcp: either the
+// service-account credentials variant OR the per-user getToken variant.
+export type DocmostMcpConfig =
+  | { apiUrl: string; email: string; password: string }
+  | { apiUrl: string; getToken: () => Promise<string> };
+
+export interface ResolvedMcpAuth {
+  config: DocmostMcpConfig;
+  // Opaque identity key bound to the MCP session for anti-fixation, or
+  // undefined when no per-user identity applies.
+  identity?: string;
+}
+
+// Narrow collaborator interfaces so this module never imports the concrete
+// AuthService/TokenService/WorkspaceRepo classes (which drag in the heavy
+// auth/space graph). McpService passes its injected instances; tests pass
+// stubs. Decouples the testable decision logic from Nest DI wiring.
+export interface McpAuthDeps {
+  apiUrl: string;
+  email?: string;
+  password?: string;
+  findWorkspace: () => Promise<{ id: string } | undefined>;
+  // Full login: mints a user session + JWT, writes the USER_LOGIN audit event
+  // and updates lastLoginAt. Called at MOST once per MCP session (at the
+  // session-init request) so we do not spam the audit log / user_sessions table
+  // on every tool call.
+  login: (
+    creds: { email: string; password: string },
+    workspaceId: string,
+  ) => Promise<string>;
+  // Non-side-effecting credential check: same lookup/password/email-verified/
+  // disabled checks as login() but mints NO session, writes NO audit row,
+  // updates NO lastLoginAt. Used for per-request anti-fixation re-validation on
+  // SUBSEQUENT requests so a correct repeat does not spawn a new DB session,
+  // while a wrong password still throws (preserving anti-fixation).
+  verifyCredentials: (
+    creds: { email: string; password: string },
+    workspaceId: string,
+  ) => Promise<void>;
+  // Bearer access-JWT verification. Verifies signature/exp/type AND (in the
+  // McpService wiring) session-active + user-not-disabled, mirroring JwtStrategy
+  // so a revoked/logged-out/disabled user with an unexpired token is rejected.
+  verifyAccessJwt: (token: string) => Promise<{ sub?: string; email?: string }>;
+  limiter: FailedLoginLimiter;
+  clientIp: string;
+  // True when this is the session-INIT request (no mcp-session-id header).
+  // INIT mints a user session via login(); SUBSEQUENT requests only re-validate
+  // credentials via verifyCredentials() (no side effects). See resolveMcp...
+  isSessionInit: boolean;
+}
+
+/**
+ * True when an error from login()/verifyCredentials() represents an actual
+ * CREDENTIALS failure (unknown email, disabled user, or wrong password) — i.e.
+ * a guessed-password signal that should count toward the brute-force limiter.
+ *
+ * It must NOT match business errors like "email not verified" (a
+ * BadRequestException), which are a legitimate 401/400 surface but not a
+ * password-guess signal — counting those would let an attacker burn a victim's
+ * limiter budget (DoS) and would dilute the brute-force signal. AuthService
+ * throws an UnauthorizedException with exactly this message for every
+ * credentials-mismatch case (no user / disabled / wrong password), so we match
+ * on that.
+ */
+export function isCredentialsFailure(err: unknown): boolean {
+  return (
+    err instanceof UnauthorizedException &&
+    typeof err.message === 'string' &&
+    err.message.toLowerCase().includes('email or password does not match')
+  );
+}
+
+// Minimal shapes for the Bearer revocation/disabled check. Kept structural so
+// this module never imports the concrete repos/JwtPayload (heavy graph).
+export interface BearerVerifyDeps {
+  // Verify signature/exp and that type === ACCESS; returns the decoded payload.
+  verifyJwt: (
+    token: string,
+  ) => Promise<{
+    sub?: string;
+    email?: string;
+    workspaceId?: string;
+    sessionId?: string;
+  }>;
+  // Load the user (or undefined) for the disabled check.
+  findUser: (
+    sub: string,
+    workspaceId: string,
+  ) => Promise<{ deactivatedAt?: Date | null; deletedAt?: Date | null } | undefined>;
+  // Load an ACTIVE (not revoked, not expired) session by id, or undefined.
+  findActiveSession: (
+    sessionId: string,
+  ) => Promise<{ userId: string; workspaceId: string } | undefined>;
+}
+
+/**
+ * Verify a /mcp Bearer access JWT to the SAME strength as JwtStrategy: not just
+ * signature/exp/type (verifyJwt), but also that the user is not disabled and —
+ * when the token carries a sessionId — that the session is still active and
+ * belongs to that user+workspace. This rejects a logged-out/revoked or disabled
+ * user who still holds an unexpired access token. Throws UnauthorizedException
+ * on any failure; never leaks why (uniform "Invalid or expired token").
+ */
+export async function verifyBearerAccess(
+  token: string,
+  deps: BearerVerifyDeps,
+): Promise<{ sub?: string; email?: string }> {
+  const generic = 'Invalid or expired token';
+  const payload = await deps.verifyJwt(token);
+
+  if (!payload.sub || !payload.workspaceId) {
+    throw new UnauthorizedException(generic);
+  }
+
+  const user = await deps.findUser(payload.sub, payload.workspaceId);
+  if (!user || user.deactivatedAt || user.deletedAt) {
+    throw new UnauthorizedException(generic);
+  }
+
+  if (payload.sessionId) {
+    const session = await deps.findActiveSession(payload.sessionId);
+    if (
+      !session ||
+      session.userId !== payload.sub ||
+      session.workspaceId !== payload.workspaceId
+    ) {
+      throw new UnauthorizedException(generic);
+    }
+  }
+
+  return { sub: payload.sub, email: payload.email };
+}
+
+/** Extract a Bearer token from an Authorization header (case-insensitive). */
+export function extractBearer(
+  authHeader: string | undefined,
+): string | undefined {
+  const [type, token] = authHeader?.split(' ') ?? [];
+  return type?.toLowerCase() === 'bearer' ? token : undefined;
+}
+
+/**
+ * Pure decision logic for the /mcp per-session identity. Precedence:
+ *   1. HTTP Basic (email:password) -> validate via `login`, issue the user's
+ *      JWT, run as that user (chosen path). Throttle FAILED logins per IP/email.
+ *   2. Authorization: Bearer <jwt> -> verify as an ACCESS JWT, run with it.
+ *   3. Env service account         -> back-compat fallback.
+ *   4. none                        -> meaningful 401.
+ *
+ * Throws UnauthorizedException with a SPECIFIC reason on failure (never a
+ * generic "MCP error"); never returns/logs the password or the Authorization
+ * header. The `JwtType.ACCESS` enforcement lives in `verifyAccessJwt`.
+ */
+export async function resolveMcpSessionConfig(
+  authHeader: string | undefined,
+  deps: McpAuthDeps,
+): Promise<ResolvedMcpAuth> {
+  const { apiUrl } = deps;
+
+  // --- 1) chosen path: Basic login/password ---
+  const basic = parseBasicAuth(authHeader);
+  if (basic) {
+    const emailLc = basic.email.toLowerCase();
+    const ipKey = `ip:${deps.clientIp}`;
+    const ipEmailKey = `ip-email:${deps.clientIp}:${emailLc}`;
+    // GLOBAL per-email key (no IP). Without this an attacker who rotates IP /
+    // X-Forwarded-For evades the per-IP and per-IP+email keys entirely and can
+    // brute a single account unthrottled. Keying one extra bucket on the email
+    // alone closes that account-brute hole regardless of source address.
+    // XFF tradeoff: clientIp is derived from the first X-Forwarded-For hop when
+    // present (see McpService.clientIp), which a client can forge when no
+    // trusted proxy is configured; the per-email global key is the part that
+    // does NOT depend on a trustworthy IP and is the real brute-force backstop.
+    const emailKey = `email:${emailLc}`;
+    if (
+      deps.limiter.isBlocked(ipKey) ||
+      deps.limiter.isBlocked(ipEmailKey) ||
+      deps.limiter.isBlocked(emailKey)
+    ) {
+      throw new UnauthorizedException(
+        'Too many failed MCP login attempts. Try again later.',
+      );
+    }
+
+    const workspace = await deps.findWorkspace();
+    if (!workspace) {
+      throw new UnauthorizedException('No workspace is configured.');
+    }
+
+    // Fix 1 (init vs subsequent):
+    //   - SESSION INIT (no mcp-session-id): full login() mints the user JWT
+    //     (the one allowed session creation + audit event for this MCP
+    //     session). The DocmostClient caches that token, so later tool calls
+    //     never re-login.
+    //   - SUBSEQUENT request (has mcp-session-id): we only need to re-validate
+    //     the caller's credentials for anti-fixation. verifyCredentials() does
+    //     the SAME lookup/password/email-verified/disabled checks as login()
+    //     but mints NO session, writes NO audit row and updates NO lastLoginAt,
+    //     so a correct repeat does not spawn a DB session per request while a
+    //     wrong password still 401s. The getToken here is never used to mint a
+    //     new session: on a subsequent request the existing session already
+    //     holds its token; this config is only consulted at init.
+    try {
+      if (deps.isSessionInit) {
+        const authToken = await deps.login(
+          { email: basic.email, password: basic.password },
+          workspace.id,
+        );
+        deps.limiter.reset(ipKey);
+        deps.limiter.reset(ipEmailKey);
+        deps.limiter.reset(emailKey);
+        return {
+          config: { apiUrl, getToken: async () => authToken },
+          identity: `basic:${emailLc}`,
+        };
+      }
+      await deps.verifyCredentials(
+        { email: basic.email, password: basic.password },
+        workspace.id,
+      );
+    } catch (err) {
+      // Only count an actual CREDENTIALS failure (wrong email/password) toward
+      // the brute-force limiter. Business errors like "email not verified" are
+      // a 401/400 surface but are NOT a guessed-password signal, so they must
+      // not let an attacker burn a victim's limiter budget or mask brute-force.
+      if (isCredentialsFailure(err)) {
+        deps.limiter.recordFailure(ipKey);
+        deps.limiter.recordFailure(ipEmailKey);
+        deps.limiter.recordFailure(emailKey);
+      }
+      const message =
+        err instanceof Error && err.message
+          ? err.message
+          : 'Email or password does not match';
+      throw new UnauthorizedException(message);
+    }
+    // Subsequent request, credentials valid: clear any prior failure budget.
+    deps.limiter.reset(ipKey);
+    deps.limiter.reset(ipEmailKey);
+    deps.limiter.reset(emailKey);
+    return {
+      config: { apiUrl, getToken: async () => '' },
+      identity: `basic:${emailLc}`,
+    };
+  }
+
+  // --- 2) fallback A: Bearer access-JWT (user-supplied token) ---
+  const bearer = extractBearer(authHeader);
+  if (bearer) {
+    let payload: { sub?: string; email?: string };
+    try {
+      payload = await deps.verifyAccessJwt(bearer);
+    } catch (err) {
+      const message =
+        err instanceof Error && err.message
+          ? err.message
+          : 'Invalid or expired token';
+      throw new UnauthorizedException(message);
+    }
+    return {
+      config: { apiUrl, getToken: async () => bearer },
+      identity: `bearer:${payload.sub ?? payload.email ?? 'unknown'}`,
+    };
+  }
+
+  // --- 3) fallback B: env service account (existing behaviour, optional) ---
+  if (deps.email && deps.password) {
+    return {
+      config: { apiUrl, email: deps.email, password: deps.password },
+      identity: 'service-account',
+    };
+  }
+
+  // --- 4) nothing usable ---
+  throw new UnauthorizedException(
+    'MCP requires HTTP Basic auth (email:password) or a Bearer access token, ' +
+      'or a configured MCP_DOCMOST_EMAIL/MCP_DOCMOST_PASSWORD service account.',
+  );
+}
+
+// Re-export JwtType so callers binding `verifyAccessJwt` know which type to
+// enforce, without importing it separately.
+export { JwtType };
diff --git a/apps/server/src/integrations/mcp/mcp.module.ts b/apps/server/src/integrations/mcp/mcp.module.ts
index 5f927d60..8ed9cb39 100644
--- a/apps/server/src/integrations/mcp/mcp.module.ts
+++ b/apps/server/src/integrations/mcp/mcp.module.ts
@@ -3,13 +3,16 @@ import { McpController } from './mcp.controller';
 import { McpService } from './mcp.service';
 import { DatabaseModule } from '@docmost/db/database.module';
 import { EnvironmentModule } from '../environment/environment.module';
+import { AuthModule } from '../../core/auth/auth.module';
+import { TokenModule } from '../../core/auth/token.module';
 
 // Community MCP feature: the server itself serves the Model Context Protocol
 // over HTTP at /mcp. DatabaseModule (global) provides WorkspaceRepo and
-// EnvironmentModule (global) provides EnvironmentService; both are imported
-// explicitly for clarity.
+// EnvironmentModule (global) provides EnvironmentService. AuthModule supplies
+// AuthService (per-user HTTP-Basic login validation) and TokenModule supplies
+// TokenService (Bearer access-JWT verification for the token fallback).
 @Module({
-  imports: [DatabaseModule, EnvironmentModule],
+  imports: [DatabaseModule, EnvironmentModule, AuthModule, TokenModule],
   controllers: [McpController],
   providers: [McpService],
 })
diff --git a/apps/server/src/integrations/mcp/mcp.service.spec.ts b/apps/server/src/integrations/mcp/mcp.service.spec.ts
new file mode 100644
index 00000000..1b4a0969
--- /dev/null
+++ b/apps/server/src/integrations/mcp/mcp.service.spec.ts
@@ -0,0 +1,396 @@
+import { BadRequestException, UnauthorizedException } from '@nestjs/common';
+import {
+  parseBasicAuth,
+  FailedLoginLimiter,
+  resolveMcpSessionConfig,
+  isCredentialsFailure,
+  verifyBearerAccess,
+  McpAuthDeps,
+} from './mcp-auth.helpers';
+
+// The /mcp per-user auth decision logic is tested through the framework-free
+// `resolveMcpSessionConfig` helper that McpService delegates to. McpService
+// itself cannot be instantiated under jest because importing AuthService drags
+// in the React email templates + queue constants graph; extracting the pure
+// logic (and wiring it in) keeps it both tested AND used (per the plan).
+
+function basicHeader(email: string, password: string): string {
+  return 'Basic ' + Buffer.from(`${email}:${password}`).toString('base64');
+}
+
+function makeDeps(over: Partial<McpAuthDeps> = {}): McpAuthDeps {
+  return {
+    apiUrl: 'http://127.0.0.1:3000/api',
+    email: over.email,
+    password: over.password,
+    findWorkspace:
+      over.findWorkspace ?? jest.fn().mockResolvedValue({ id: 'ws-1' }),
+    login: over.login ?? jest.fn().mockResolvedValue('issued-user-jwt'),
+    verifyCredentials:
+      over.verifyCredentials ?? jest.fn().mockResolvedValue(undefined),
+    verifyAccessJwt:
+      over.verifyAccessJwt ??
+      jest.fn().mockResolvedValue({ sub: 'user-1', email: 'u@e.com' }),
+    limiter: over.limiter ?? new FailedLoginLimiter(5, 60_000),
+    clientIp: over.clientIp ?? '10.0.0.1',
+    // Default to the session-INIT request (no mcp-session-id) so existing
+    // assertions about login() being called keep their meaning.
+    isSessionInit: over.isSessionInit ?? true,
+  };
+}
+
+describe('parseBasicAuth', () => {
+  it('decodes email:password', () => {
+    expect(parseBasicAuth(basicHeader('a@b.com', 'pw'))).toEqual({
+      email: 'a@b.com',
+      password: 'pw',
+    });
+  });
+
+  it('splits on the FIRST colon so passwords may contain colons', () => {
+    expect(parseBasicAuth(basicHeader('a@b.com', 'p:w:x'))).toEqual({
+      email: 'a@b.com',
+      password: 'p:w:x',
+    });
+  });
+
+  it('returns null for non-Basic / malformed headers', () => {
+    expect(parseBasicAuth(undefined)).toBeNull();
+    expect(parseBasicAuth('Bearer xyz')).toBeNull();
+    expect(
+      parseBasicAuth('Basic ' + Buffer.from('nocolon').toString('base64')),
+    ).toBeNull();
+  });
+
+  it('returns null when the email part is empty (":password")', () => {
+    expect(
+      parseBasicAuth('Basic ' + Buffer.from(':pw').toString('base64')),
+    ).toBeNull();
+  });
+});
+
+describe('isCredentialsFailure', () => {
+  it('is true for the credentials-mismatch UnauthorizedException', () => {
+    expect(
+      isCredentialsFailure(
+        new UnauthorizedException('Email or password does not match'),
+      ),
+    ).toBe(true);
+  });
+
+  it('is false for business errors like email-not-verified', () => {
+    expect(
+      isCredentialsFailure(
+        new BadRequestException('Please verify your email address.'),
+      ),
+    ).toBe(false);
+    expect(isCredentialsFailure(new Error('boom'))).toBe(false);
+  });
+});
+
+describe('FailedLoginLimiter', () => {
+  it('blocks after threshold failures within the window; reset clears it', () => {
+    const lim = new FailedLoginLimiter(3, 1000);
+    const k = 'ip:1.2.3.4';
+    expect(lim.isBlocked(k, 0)).toBe(false);
+    lim.recordFailure(k, 0);
+    lim.recordFailure(k, 0);
+    expect(lim.isBlocked(k, 0)).toBe(false);
+    lim.recordFailure(k, 0);
+    expect(lim.isBlocked(k, 0)).toBe(true);
+    lim.reset(k);
+    expect(lim.isBlocked(k, 0)).toBe(false);
+  });
+
+  it('rolls over after the window', () => {
+    const lim = new FailedLoginLimiter(1, 1000);
+    const k = 'ip:1.2.3.4';
+    lim.recordFailure(k, 0);
+    expect(lim.isBlocked(k, 0)).toBe(true);
+    expect(lim.isBlocked(k, 1000)).toBe(false);
+  });
+});
+
+describe('verifyBearerAccess (Bearer revocation/disabled checks)', () => {
+  const goodPayload = {
+    sub: 'user-1',
+    email: 'u@e.com',
+    workspaceId: 'ws-1',
+    sessionId: 'sess-1',
+  };
+
+  function bearerDeps(over: Partial<Parameters<typeof verifyBearerAccess>[1]> = {}) {
+    return {
+      verifyJwt: over.verifyJwt ?? jest.fn().mockResolvedValue(goodPayload),
+      findUser:
+        over.findUser ?? jest.fn().mockResolvedValue({ deactivatedAt: null }),
+      findActiveSession:
+        over.findActiveSession ??
+        jest
+          .fn()
+          .mockResolvedValue({ userId: 'user-1', workspaceId: 'ws-1' }),
+    };
+  }
+
+  it('valid token + active session + enabled user -> resolves identity', async () => {
+    const res = await verifyBearerAccess('t', bearerDeps());
+    expect(res).toEqual({ sub: 'user-1', email: 'u@e.com' });
+  });
+
+  it('rejects when the session is no longer active (logged out / revoked)', async () => {
+    await expect(
+      verifyBearerAccess(
+        't',
+        bearerDeps({ findActiveSession: jest.fn().mockResolvedValue(undefined) }),
+      ),
+    ).rejects.toThrow(UnauthorizedException);
+  });
+
+  it('rejects when the session belongs to a different user', async () => {
+    await expect(
+      verifyBearerAccess(
+        't',
+        bearerDeps({
+          findActiveSession: jest
+            .fn()
+            .mockResolvedValue({ userId: 'other', workspaceId: 'ws-1' }),
+        }),
+      ),
+    ).rejects.toThrow(UnauthorizedException);
+  });
+
+  it('rejects when the user is disabled (deactivated/deleted)', async () => {
+    await expect(
+      verifyBearerAccess(
+        't',
+        bearerDeps({
+          findUser: jest.fn().mockResolvedValue({ deactivatedAt: new Date() }),
+        }),
+      ),
+    ).rejects.toThrow(UnauthorizedException);
+    await expect(
+      verifyBearerAccess(
+        't',
+        bearerDeps({ findUser: jest.fn().mockResolvedValue(undefined) }),
+      ),
+    ).rejects.toThrow(UnauthorizedException);
+  });
+
+  it('propagates a verifyJwt failure (bad signature/exp/type)', async () => {
+    await expect(
+      verifyBearerAccess(
+        't',
+        bearerDeps({
+          verifyJwt: jest
+            .fn()
+            .mockRejectedValue(new UnauthorizedException('jwt expired')),
+        }),
+      ),
+    ).rejects.toThrow('jwt expired');
+  });
+});
+
+describe('resolveMcpSessionConfig', () => {
+  it('Basic good creds -> calls login with the default workspace, returns a getToken config', async () => {
+    const login = jest.fn().mockResolvedValue('issued-user-jwt');
+    const findWorkspace = jest.fn().mockResolvedValue({ id: 'ws-1' });
+    const resolved = await resolveMcpSessionConfig(
+      basicHeader('user@example.com', 'pw'),
+      makeDeps({ login, findWorkspace }),
+    );
+    expect(findWorkspace).toHaveBeenCalled();
+    expect(login).toHaveBeenCalledWith(
+      { email: 'user@example.com', password: 'pw' },
+      'ws-1',
+    );
+    expect('getToken' in resolved.config).toBe(true);
+    const cfg = resolved.config as { getToken: () => Promise<string> };
+    await expect(cfg.getToken()).resolves.toBe('issued-user-jwt');
+    expect(resolved.identity).toBe('basic:user@example.com');
+  });
+
+  it('Basic password containing a colon is split on the first colon', async () => {
+    const login = jest.fn().mockResolvedValue('jwt');
+    await resolveMcpSessionConfig(
+      basicHeader('user@example.com', 'a:b:c'),
+      makeDeps({ login }),
+    );
+    expect(login).toHaveBeenCalledWith(
+      { email: 'user@example.com', password: 'a:b:c' },
+      'ws-1',
+    );
+  });
+
+  it('Basic bad creds -> specific 401 (not generic) and increments the limiter', async () => {
+    const limiter = new FailedLoginLimiter(5, 60_000);
+    const login = jest
+      .fn()
+      .mockRejectedValue(
+        new UnauthorizedException('Email or password does not match'),
+      );
+    const deps = makeDeps({ login, limiter });
+
+    await expect(
+      resolveMcpSessionConfig(basicHeader('user@example.com', 'wrong'), deps),
+    ).rejects.toThrow('Email or password does not match');
+    // The failure was recorded; drive to the threshold (5) -> throttled message.
+    for (let i = 0; i < 4; i++) {
+      await resolveMcpSessionConfig(
+        basicHeader('user@example.com', 'wrong'),
+        deps,
+      ).catch(() => undefined);
+    }
+    await expect(
+      resolveMcpSessionConfig(basicHeader('user@example.com', 'wrong'), deps),
+    ).rejects.toThrow(/Too many failed MCP login attempts/);
+  });
+
+  it('Bearer -> verifies as ACCESS and returns a getToken config', async () => {
+    const verifyAccessJwt = jest
+      .fn()
+      .mockResolvedValue({ sub: 'user-9', email: 'u@e.com' });
+    const resolved = await resolveMcpSessionConfig(
+      'Bearer some.jwt.value',
+      makeDeps({ verifyAccessJwt }),
+    );
+    expect(verifyAccessJwt).toHaveBeenCalledWith('some.jwt.value');
+    const cfg = resolved.config as { getToken: () => Promise<string> };
+    await expect(cfg.getToken()).resolves.toBe('some.jwt.value');
+    expect(resolved.identity).toBe('bearer:user-9');
+  });
+
+  it('Bearer invalid -> specific 401 from verifyAccessJwt', async () => {
+    const verifyAccessJwt = jest
+      .fn()
+      .mockRejectedValue(new UnauthorizedException('jwt expired'));
+    await expect(
+      resolveMcpSessionConfig('Bearer expired', makeDeps({ verifyAccessJwt })),
+    ).rejects.toThrow('jwt expired');
+  });
+
+  it('no creds + env service account configured -> service-account config', async () => {
+    const resolved = await resolveMcpSessionConfig(
+      undefined,
+      makeDeps({ email: 'svc@example.com', password: 'svcpw' }),
+    );
+    expect('email' in resolved.config).toBe(true);
+    const cfg = resolved.config as { email: string; password: string };
+    expect(cfg.email).toBe('svc@example.com');
+    expect(cfg.password).toBe('svcpw');
+    expect(resolved.identity).toBe('service-account');
+  });
+
+  it('no creds + no env service account -> meaningful 401 listing accepted methods', async () => {
+    await expect(
+      resolveMcpSessionConfig(undefined, makeDeps()),
+    ).rejects.toThrow(/HTTP Basic auth.*Bearer access token.*service account/s);
+  });
+
+  it('SESSION INIT Basic -> mints a session via login() (verifyCredentials NOT called)', async () => {
+    const login = jest.fn().mockResolvedValue('issued-user-jwt');
+    const verifyCredentials = jest.fn().mockResolvedValue(undefined);
+    const resolved = await resolveMcpSessionConfig(
+      basicHeader('user@example.com', 'pw'),
+      makeDeps({ login, verifyCredentials, isSessionInit: true }),
+    );
+    expect(login).toHaveBeenCalledTimes(1);
+    expect(verifyCredentials).not.toHaveBeenCalled();
+    const cfg = resolved.config as { getToken: () => Promise<string> };
+    await expect(cfg.getToken()).resolves.toBe('issued-user-jwt');
+    expect(resolved.identity).toBe('basic:user@example.com');
+  });
+
+  it('SUBSEQUENT Basic correct creds -> uses verifyCredentials, NEVER login() (no new session/audit), same identity', async () => {
+    const login = jest.fn().mockResolvedValue('issued-user-jwt');
+    const verifyCredentials = jest.fn().mockResolvedValue(undefined);
+    const resolved = await resolveMcpSessionConfig(
+      basicHeader('user@example.com', 'pw'),
+      makeDeps({ login, verifyCredentials, isSessionInit: false }),
+    );
+    // The side-effecting login() (audit + lastLoginAt + user_sessions insert)
+    // is NOT hit on a subsequent request: only the non-side-effecting verify.
+    expect(login).not.toHaveBeenCalled();
+    expect(verifyCredentials).toHaveBeenCalledWith(
+      { email: 'user@example.com', password: 'pw' },
+      'ws-1',
+    );
+    // Identity still matches the init identity so anti-fixation accepts it.
+    expect(resolved.identity).toBe('basic:user@example.com');
+  });
+
+  it('SUBSEQUENT Basic wrong password -> still 401 (anti-fixation), without minting a session', async () => {
+    const login = jest.fn().mockResolvedValue('issued-user-jwt');
+    const verifyCredentials = jest
+      .fn()
+      .mockRejectedValue(
+        new UnauthorizedException('Email or password does not match'),
+      );
+    await expect(
+      resolveMcpSessionConfig(
+        basicHeader('user@example.com', 'wrong'),
+        makeDeps({ login, verifyCredentials, isSessionInit: false }),
+      ),
+    ).rejects.toThrow('Email or password does not match');
+    expect(login).not.toHaveBeenCalled();
+  });
+
+  it('global per-email limiter key blocks an attacker rotating IP/XFF for one account', async () => {
+    const limiter = new FailedLoginLimiter(5, 60_000);
+    const login = jest
+      .fn()
+      .mockRejectedValue(
+        new UnauthorizedException('Email or password does not match'),
+      );
+    // 5 failures against the SAME email but DIFFERENT IPs each time. The per-IP
+    // and per-IP+email keys never accumulate, but the global per-email key does.
+    for (let i = 0; i < 5; i++) {
+      await resolveMcpSessionConfig(
+        basicHeader('victim@example.com', 'wrong'),
+        makeDeps({ login, limiter, clientIp: `10.0.0.${i}` }),
+      ).catch(() => undefined);
+    }
+    // A 6th attempt from yet another fresh IP is now throttled purely by the
+    // email key — proving IP/XFF rotation no longer evades the limiter.
+    await expect(
+      resolveMcpSessionConfig(
+        basicHeader('victim@example.com', 'wrong'),
+        makeDeps({ login, limiter, clientIp: '10.0.0.99' }),
+      ),
+    ).rejects.toThrow(/Too many failed MCP login attempts/);
+  });
+
+  it('limiter does NOT count business errors (email not verified) as a failed login', async () => {
+    const limiter = new FailedLoginLimiter(1, 60_000);
+    const login = jest
+      .fn()
+      .mockRejectedValue(
+        new BadRequestException('Please verify your email address.'),
+      );
+    const deps = () =>
+      makeDeps({ login, limiter, clientIp: '10.0.0.7' });
+    // First attempt: business error, surfaced as 401, but must NOT increment.
+    await resolveMcpSessionConfig(
+      basicHeader('user@example.com', 'pw'),
+      deps(),
+    ).catch(() => undefined);
+    // With threshold 1, if it had counted, the next attempt would be throttled.
+    // Instead it should reach login() again (same business error, NOT throttle).
+    await expect(
+      resolveMcpSessionConfig(basicHeader('user@example.com', 'pw'), deps()),
+    ).rejects.toThrow(/verify your email/);
+  });
+
+  it('anti-fixation: different users yield different identity keys (compared by the http identify hook)', async () => {
+    const a = await resolveMcpSessionConfig(
+      basicHeader('alice@example.com', 'pw'),
+      makeDeps(),
+    );
+    const b = await resolveMcpSessionConfig(
+      basicHeader('bob@example.com', 'pw'),
+      makeDeps(),
+    );
+    expect(a.identity).toBe('basic:alice@example.com');
+    expect(b.identity).toBe('basic:bob@example.com');
+    expect(a.identity).not.toBe(b.identity);
+  });
+});
diff --git a/apps/server/src/integrations/mcp/mcp.service.ts b/apps/server/src/integrations/mcp/mcp.service.ts
index be67e228..a18e2d6d 100644
--- a/apps/server/src/integrations/mcp/mcp.service.ts
+++ b/apps/server/src/integrations/mcp/mcp.service.ts
@@ -1,8 +1,26 @@
-import { Injectable, Logger } from '@nestjs/common';
+import {
+  Injectable,
+  Logger,
+  UnauthorizedException,
+} from '@nestjs/common';
 import { pathToFileURL } from 'node:url';
+import { timingSafeEqual } from 'node:crypto';
+import { IncomingMessage } from 'node:http';
 import { FastifyReply, FastifyRequest } from 'fastify';
 import { EnvironmentService } from '../environment/environment.service';
 import { WorkspaceRepo } from '@docmost/db/repos/workspace/workspace.repo';
+import { UserRepo } from '@docmost/db/repos/user/user.repo';
+import { UserSessionRepo } from '@docmost/db/repos/session/user-session.repo';
+import { AuthService } from '../../core/auth/services/auth.service';
+import { TokenService } from '../../core/auth/services/token.service';
+import { JwtType, JwtPayload } from '../../core/auth/dto/jwt-payload';
+import {
+  FailedLoginLimiter,
+  resolveMcpSessionConfig,
+  verifyBearerAccess,
+  DocmostMcpConfig,
+  ResolvedMcpAuth,
+} from './mcp-auth.helpers';
 
 // Minimal shape of the embedded MCP HTTP handler exported by @docmost/mcp/http.
 interface McpHttpHandler {
@@ -13,14 +31,23 @@ interface McpHttpHandler {
   ): Promise<void>;
 }
 
+type McpConfigResolver = (
+  req: IncomingMessage,
+) => DocmostMcpConfig | Promise<DocmostMcpConfig>;
+
 interface McpHttpModule {
-  createMcpHttpHandler(config: {
-    apiUrl: string;
-    email: string;
-    password: string;
-  }): McpHttpHandler;
+  createMcpHttpHandler(
+    config: DocmostMcpConfig | McpConfigResolver,
+    options?: { identify?: (req: IncomingMessage) => string | Promise<string> },
+  ): McpHttpHandler;
 }
 
+// Stash key for the per-request resolved config/identity computed (and
+// validated) in handle() BEFORE res.hijack(), then read back by the resolver
+// the MCP package invokes. Doing the validation pre-hijack lets a bad-creds
+// failure return a clean 401 JSON instead of tearing a hijacked response.
+const MCP_RESOLVED = Symbol('mcpResolvedConfig');
+
 // TS with module:commonjs downlevels a literal import() to require(), which
 // cannot load the ESM-only @docmost/mcp package. Indirect through Function so
 // the real dynamic import() survives compilation and can load ESM from
@@ -37,13 +64,23 @@ export class McpService {
   private handlerPromise: Promise<McpHttpHandler> | null = null;
   private warnedMissingCreds = false;
 
+  // In-memory per-IP/email throttle for FAILED /mcp Basic logins. Calling
+  // AuthService.login directly bypasses the controller's ThrottlerGuard, so
+  // this is the brute-force speed bump for /mcp. 5 failures per 60s window.
+  private readonly failedLogins = new FailedLoginLimiter(5, 60_000);
+
   constructor(
     private readonly environmentService: EnvironmentService,
     private readonly workspaceRepo: WorkspaceRepo,
+    private readonly authService: AuthService,
+    private readonly tokenService: TokenService,
+    private readonly userRepo: UserRepo,
+    private readonly userSessionRepo: UserSessionRepo,
   ) {}
 
   // Service account the embedded MCP uses to talk back to this Docmost
-  // instance over loopback REST + the collaboration WebSocket.
+  // instance over loopback REST + the collaboration WebSocket. Now OPTIONAL:
+  // it is only a fallback when no per-user Basic/Bearer credentials are sent.
   private getEmail(): string | undefined {
     return process.env.MCP_DOCMOST_EMAIL;
   }
@@ -80,8 +117,102 @@ export class McpService {
     }
   }
 
+  // Constant-time comparison of the optional shared X-MCP-Token guard. A header
+  // value may arrive as string | string[] (multiple X-MCP-Token headers), so we
+  // normalise to the first string. crypto.timingSafeEqual avoids leaking the
+  // token's length-prefix via early-exit string comparison; it requires equal
+  // buffer lengths, so a length mismatch is treated as a non-match WITHOUT
+  // calling timingSafeEqual (which would throw on unequal lengths).
+  private sharedTokenMatches(
+    expected: string,
+    provided: string | string[] | undefined,
+  ): boolean {
+    const value = Array.isArray(provided) ? provided[0] : provided;
+    if (typeof value !== 'string') return false;
+    const a = Buffer.from(value);
+    const b = Buffer.from(expected);
+    if (a.length !== b.length) return false;
+    return timingSafeEqual(a, b);
+  }
+
+  // Best-effort client IP for the failed-login limiter key. Prefer Fastify's
+  // req.ip (which honours a configured trustProxy chain) and the socket address
+  // over a raw X-Forwarded-For hop, since XFF is client-forgeable when no
+  // trusted proxy is configured. The first XFF hop is only used as a last
+  // resort. NOTE: a forged IP can only dodge the per-IP limiter keys — the
+  // GLOBAL per-email key in resolveMcpSessionConfig is the real account-brute
+  // backstop and does not depend on this value.
+  private clientIp(req: FastifyRequest): string {
+    if (req.ip) return req.ip;
+    if (req.socket?.remoteAddress) return req.socket.remoteAddress;
+    const xff = req.headers['x-forwarded-for'];
+    if (typeof xff === 'string' && xff.length > 0) {
+      return xff.split(',')[0].trim();
+    }
+    return 'unknown';
+  }
+
+  // Bearer access-JWT verification for the /mcp token fallback. verifyJwt only
+  // checks signature/exp/type, but a logged-out (revoked) or disabled user can
+  // still hold an unexpired access JWT. JwtStrategy additionally checks the
+  // session is active and the user is not disabled; we mirror those exact checks
+  // here so the MCP Bearer path is not weaker than the normal cookie/header path.
+  private async verifyMcpBearer(
+    token: string,
+  ): Promise<{ sub?: string; email?: string }> {
+    // The revocation/disabled decision logic lives in the framework-free
+    // verifyBearerAccess helper (unit-testable without the heavy auth graph);
+    // this method only wires in the concrete TokenService + repos.
+    return verifyBearerAccess(token, {
+      verifyJwt: (t) =>
+        this.tokenService.verifyJwt(t, JwtType.ACCESS) as Promise<JwtPayload>,
+      findUser: (sub, workspaceId) =>
+        this.userRepo.findById(sub, workspaceId),
+      findActiveSession: (sessionId) =>
+        this.userSessionRepo.findActiveById(sessionId),
+    });
+  }
+
+  /**
+   * Resolve the per-session identity from the request and produce the
+   * DocmostMcpConfig the MCP package will run under, plus an opaque identity
+   * key for anti-fixation. The decision logic lives in the framework-free
+   * `resolveMcpSessionConfig` helper (so it is unit-testable without the heavy
+   * auth graph); this method only wires McpService's injected collaborators in.
+   *
+   * Throws UnauthorizedException with a SPECIFIC message on failure (never a
+   * generic "MCP error"); never logs/echoes the password or Authorization
+   * header. Run BEFORE res.hijack() so the 401 is clean JSON.
+   */
+  async resolveSessionConfig(req: FastifyRequest): Promise<ResolvedMcpAuth> {
+    const authHeader = req.headers['authorization'] as string | undefined;
+    // A request carrying an mcp-session-id is operating on an ALREADY
+    // established session (see packages/mcp/src/http.ts: a new session is only
+    // minted by an initialize POST with no session id). Only the INIT request
+    // should run the full, session-minting login(); subsequent requests only
+    // re-validate credentials (anti-fixation) with no side effects.
+    const isSessionInit = !req.headers['mcp-session-id'];
+    return resolveMcpSessionConfig(authHeader, {
+      apiUrl: this.getApiUrl(),
+      email: this.getEmail(),
+      password: this.getPassword(),
+      findWorkspace: () => this.workspaceRepo.findFirst(),
+      login: (creds, workspaceId) => this.authService.login(creds, workspaceId),
+      verifyCredentials: async (creds, workspaceId) => {
+        await this.authService.verifyUserCredentials(creds, workspaceId);
+      },
+      verifyAccessJwt: (token) => this.verifyMcpBearer(token),
+      limiter: this.failedLogins,
+      clientIp: this.clientIp(req),
+      isSessionInit,
+    });
+  }
+
   // Lazily create the HTTP handler exactly once. The import is indirected so
   // the ESM-only @docmost/mcp package can be loaded from this CommonJS module.
+  // The handler is created with a per-request RESOLVER (and an `identify` hook
+  // for anti-fixation): both read the auth that handle() resolved and stashed
+  // on req before hijack, so the package never re-parses credentials.
   private async getHandler(): Promise<McpHttpHandler> {
     if (this.handler) {
       return this.handler;
@@ -95,11 +226,29 @@ export class McpService {
         const mod = (await esmImport(
           pathToFileURL(httpEntry).href,
         )) as McpHttpModule;
-        const handler = mod.createMcpHttpHandler({
-          apiUrl: this.getApiUrl(),
-          email: this.getEmail()!,
-          password: this.getPassword()!,
-        });
+        const handler = mod.createMcpHttpHandler(
+          (req: IncomingMessage) => {
+            const resolved = (req as unknown as Record<symbol, unknown>)[
+              MCP_RESOLVED
+            ] as ResolvedMcpAuth | undefined;
+            if (!resolved) {
+              // Should never happen: handle() always stashes before delegating.
+              throw new UnauthorizedException('MCP authentication missing.');
+            }
+            return resolved.config;
+          },
+          {
+            identify: (req: IncomingMessage) => {
+              const resolved = (req as unknown as Record<symbol, unknown>)[
+                MCP_RESOLVED
+              ] as ResolvedMcpAuth | undefined;
+              if (!resolved || resolved.identity === undefined) {
+                throw new UnauthorizedException('MCP authentication missing.');
+              }
+              return resolved.identity;
+            },
+          },
+        );
         this.handler = handler;
         return handler;
       })().catch((err) => {
@@ -112,13 +261,13 @@ export class McpService {
   }
 
   async handle(req: FastifyRequest, res: FastifyReply): Promise<void> {
-    // Optional static bearer-token guard. When MCP_TOKEN is set, the request
-    // must carry a matching `Authorization: Bearer <token>` header. When unset,
-    // /mcp relies on the workspace toggle and network isolation (no auth).
-    const token = process.env.MCP_TOKEN;
-    if (token) {
-      const authHeader = req.headers['authorization'];
-      if (authHeader !== `Bearer ${token}`) {
+    // Optional shared-guard. When MCP_TOKEN is set, the request must carry a
+    // matching `X-MCP-Token` header. It now lives in its OWN header so it never
+    // collides with `Authorization`, which carries the per-user credentials.
+    const sharedToken = process.env.MCP_TOKEN;
+    if (sharedToken) {
+      const provided = req.headers['x-mcp-token'];
+      if (!this.sharedTokenMatches(sharedToken, provided)) {
         res.status(401).send({ error: 'Unauthorized' });
         return;
       }
@@ -129,20 +278,40 @@ export class McpService {
       return;
     }
 
-    if (!this.credsConfigured()) {
-      if (!this.warnedMissingCreds) {
-        this.warnedMissingCreds = true;
-        this.logger.warn(
-          'MCP is enabled but not configured: set MCP_DOCMOST_EMAIL and MCP_DOCMOST_PASSWORD.',
-        );
+    // Resolve + validate the per-session identity BEFORE hijacking the response
+    // so bad credentials surface as a clean 401 JSON (never a torn response and
+    // never a generic "MCP error"). The resolved config/identity is stashed on
+    // the raw request for the package's resolver + identify hook to read back.
+    let resolved: ResolvedMcpAuth;
+    try {
+      resolved = await this.resolveSessionConfig(req);
+    } catch (err) {
+      if (err instanceof UnauthorizedException) {
+        // Warn once if the only thing missing is the service account, to keep
+        // the original operator hint.
+        if (
+          !this.credsConfigured() &&
+          !req.headers['authorization'] &&
+          !this.warnedMissingCreds
+        ) {
+          this.warnedMissingCreds = true;
+          this.logger.warn(
+            'MCP is enabled but received a request with no credentials and no ' +
+              'MCP_DOCMOST_EMAIL/MCP_DOCMOST_PASSWORD service account configured.',
+          );
+        }
+        res.status(401).send({ error: err.message });
+        return;
       }
-      res.status(503).send({
-        error:
-          'MCP is not configured (set MCP_DOCMOST_EMAIL / MCP_DOCMOST_PASSWORD)',
-      });
+      this.logger.error('MCP auth resolution failed', err as Error);
+      res.status(500).send({ error: 'Internal server error' });
       return;
     }
 
+    // Stash the resolved auth on the raw request so the package's resolver +
+    // identify hook (wired in getHandler) read it back instead of re-parsing.
+    (req.raw as unknown as Record<symbol, unknown>)[MCP_RESOLVED] = resolved;
+
     // Hand the raw Node req/res to the MCP transport. hijack() tells Fastify
     // to stop managing this response so the transport can write to it directly.
     res.hijack();
diff --git a/packages/mcp/build/http.js b/packages/mcp/build/http.js
index f22cc694..45c422b0 100644
--- a/packages/mcp/build/http.js
+++ b/packages/mcp/build/http.js
@@ -7,12 +7,30 @@ import { createDocmostMcpServer } from "./index.js";
  * embedding host (the gitmost NestJS server) bridges its raw Node req/res into
  * `handleRequest`. One McpServer + transport is created per MCP session and
  * kept alive between requests, keyed by the `mcp-session-id` header.
+ *
+ * `config` is EITHER a static `DocmostMcpConfig` (back-compat: stdio + the env
+ * service account, unchanged) OR a `McpConfigResolver` run once per session at
+ * `initialize` to bind that session to the request's identity.
  */
-export function createMcpHttpHandler(config) {
+export function createMcpHttpHandler(config, options = {}) {
     // One transport (and one McpServer) per MCP session, keyed by session id.
     const transports = {};
     // Last activity timestamp per session id, used for idle eviction.
     const lastSeen = {};
+    // Anti-session-fixation: the opaque identity key bound to each session at
+    // initialize. A later request for that session whose key differs is rejected.
+    const sessionIdentity = {};
+    // Write a JSON-RPC error and end the response. Used for the 400/401 paths so
+    // every early rejection is a well-formed JSON-RPC error, not a torn response.
+    const sendJsonRpcError = (res, statusCode, code, message) => {
+        res.statusCode = statusCode;
+        res.setHeader("Content-Type", "application/json");
+        res.end(JSON.stringify({
+            jsonrpc: "2.0",
+            error: { code, message },
+            id: null,
+        }));
+    };
     // Idle session TTL (ms): a session with no activity for this long is evicted.
     // Defaults to 30 min; overridable via MCP_SESSION_IDLE_MS.
     const idleTtlMs = (() => {
@@ -29,6 +47,7 @@ export function createMcpHttpHandler(config) {
             if (now - (lastSeen[sid] ?? 0) > idleTtlMs) {
                 void transports[sid].close();
                 delete lastSeen[sid];
+                delete sessionIdentity[sid];
             }
         }
     }, sweepIntervalMs);
@@ -41,16 +60,23 @@ export function createMcpHttpHandler(config) {
             // A new session may only be created by an initialize request without a
             // session id.
             if (sessionId || !isInitializeRequest(parsedBody)) {
-                res.statusCode = 400;
-                res.setHeader("Content-Type", "application/json");
-                res.end(JSON.stringify({
-                    jsonrpc: "2.0",
-                    error: {
-                        code: -32000,
-                        message: "Bad Request: no valid session ID provided",
-                    },
-                    id: null,
-                }));
+                sendJsonRpcError(res, 400, -32000, "Bad Request: no valid session ID provided");
+                return;
+            }
+            // Resolve the per-session config from the request (per-user identity) when
+            // a resolver was supplied; otherwise use the static config unchanged. The
+            // resolver may throw (e.g. bad credentials) — surface a clean 401, never
+            // a created session.
+            let sessionConfig;
+            let identity;
+            try {
+                sessionConfig =
+                    typeof config === "function" ? await config(req) : config;
+                if (options.identify)
+                    identity = await options.identify(req);
+            }
+            catch (err) {
+                sendJsonRpcError(res, 401, -32001, err instanceof Error ? err.message : "Unauthorized");
                 return;
             }
             transport = new StreamableHTTPServerTransport({
@@ -58,31 +84,46 @@ export function createMcpHttpHandler(config) {
                 onsessioninitialized: (sid) => {
                     transports[sid] = transport;
                     lastSeen[sid] = Date.now();
+                    // Bind the resolved identity to the new session id for anti-fixation.
+                    if (identity !== undefined)
+                        sessionIdentity[sid] = identity;
                 },
             });
             transport.onclose = () => {
                 const sid = transport.sessionId;
                 if (sid && transports[sid])
                     delete transports[sid];
+                if (sid)
+                    delete sessionIdentity[sid];
             };
-            const server = createDocmostMcpServer(config);
+            const server = createDocmostMcpServer(sessionConfig);
             await server.connect(transport);
             await transport.handleRequest(req, res, parsedBody);
             return;
         }
         if (!transport) {
-            res.statusCode = 400;
-            res.setHeader("Content-Type", "application/json");
-            res.end(JSON.stringify({
-                jsonrpc: "2.0",
-                error: {
-                    code: -32000,
-                    message: "Bad Request: no valid session ID provided",
-                },
-                id: null,
-            }));
+            sendJsonRpcError(res, 400, -32000, "Bad Request: no valid session ID provided");
             return;
         }
+        // Anti-session-fixation: a request reusing an existing session id must
+        // present credentials/token that resolve to the SAME identity bound at
+        // initialize, otherwise reject with 401. This prevents hijacking another
+        // user's established session by replaying its session id with different
+        // credentials.
+        if (options.identify && sessionId && sessionId in sessionIdentity) {
+            let presented;
+            try {
+                presented = await options.identify(req);
+            }
+            catch (err) {
+                sendJsonRpcError(res, 401, -32001, err instanceof Error ? err.message : "Unauthorized");
+                return;
+            }
+            if (presented !== sessionIdentity[sessionId]) {
+                sendJsonRpcError(res, 401, -32001, "Credentials do not match the user that owns this MCP session.");
+                return;
+            }
+        }
         // Routing to an existing transport: refresh its idle timestamp.
         if (sessionId)
             lastSeen[sessionId] = Date.now();
diff --git a/packages/mcp/src/http.ts b/packages/mcp/src/http.ts
index b05bdfbf..cc344093 100644
--- a/packages/mcp/src/http.ts
+++ b/packages/mcp/src/http.ts
@@ -4,17 +4,71 @@ import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/
 import { isInitializeRequest } from "@modelcontextprotocol/sdk/types.js";
 import { createDocmostMcpServer, DocmostMcpConfig } from "./index.js";
 
+/**
+ * Per-request config resolver. Run ONCE per MCP session, at the `initialize`
+ * POST, so the session's DocmostClient is bound to that request's identity
+ * (e.g. the HTTP-Basic user the embedding host validated). Back-compat: a plain
+ * `DocmostMcpConfig` object is still accepted (stdio + service account), in
+ * which case the resolver branch is never taken.
+ */
+export type McpConfigResolver = (
+  req: IncomingMessage,
+) => DocmostMcpConfig | Promise<DocmostMcpConfig>;
+
+/**
+ * Optional anti-session-fixation hook. When supplied, it is called on EVERY
+ * request (init and subsequent) to derive an opaque identity key for the
+ * presented credentials/token. The key resolved at session init is bound to the
+ * `mcp-session-id`; a later request whose key differs is rejected with 401, so
+ * a caller cannot hijack another user's established session by reusing its
+ * session id with different credentials. The key is opaque to this package (the
+ * embedding host decides what identity means, e.g. the user's `sub`/email), so
+ * the package stays generic. Throwing here surfaces as a 401 as well.
+ */
+export interface McpHttpOptions {
+  identify?: (req: IncomingMessage) => string | Promise<string>;
+}
+
 /**
  * Build a stateful Streamable-HTTP handler for the Docmost MCP server. The
  * embedding host (the gitmost NestJS server) bridges its raw Node req/res into
  * `handleRequest`. One McpServer + transport is created per MCP session and
  * kept alive between requests, keyed by the `mcp-session-id` header.
+ *
+ * `config` is EITHER a static `DocmostMcpConfig` (back-compat: stdio + the env
+ * service account, unchanged) OR a `McpConfigResolver` run once per session at
+ * `initialize` to bind that session to the request's identity.
  */
-export function createMcpHttpHandler(config: DocmostMcpConfig) {
+export function createMcpHttpHandler(
+  config: DocmostMcpConfig | McpConfigResolver,
+  options: McpHttpOptions = {},
+) {
   // One transport (and one McpServer) per MCP session, keyed by session id.
   const transports: Record<string, StreamableHTTPServerTransport> = {};
   // Last activity timestamp per session id, used for idle eviction.
   const lastSeen: Record<string, number> = {};
+  // Anti-session-fixation: the opaque identity key bound to each session at
+  // initialize. A later request for that session whose key differs is rejected.
+  const sessionIdentity: Record<string, string> = {};
+
+  // Write a JSON-RPC error and end the response. Used for the 400/401 paths so
+  // every early rejection is a well-formed JSON-RPC error, not a torn response.
+  const sendJsonRpcError = (
+    res: ServerResponse,
+    statusCode: number,
+    code: number,
+    message: string,
+  ): void => {
+    res.statusCode = statusCode;
+    res.setHeader("Content-Type", "application/json");
+    res.end(
+      JSON.stringify({
+        jsonrpc: "2.0",
+        error: { code, message },
+        id: null,
+      }),
+    );
+  };
 
   // Idle session TTL (ms): a session with no activity for this long is evicted.
   // Defaults to 30 min; overridable via MCP_SESSION_IDLE_MS.
@@ -33,6 +87,7 @@ export function createMcpHttpHandler(config: DocmostMcpConfig) {
       if (now - (lastSeen[sid] ?? 0) > idleTtlMs) {
         void transports[sid].close();
         delete lastSeen[sid];
+        delete sessionIdentity[sid];
       }
     }
   }, sweepIntervalMs);
@@ -51,17 +106,30 @@ export function createMcpHttpHandler(config: DocmostMcpConfig) {
       // A new session may only be created by an initialize request without a
       // session id.
       if (sessionId || !isInitializeRequest(parsedBody)) {
-        res.statusCode = 400;
-        res.setHeader("Content-Type", "application/json");
-        res.end(
-          JSON.stringify({
-            jsonrpc: "2.0",
-            error: {
-              code: -32000,
-              message: "Bad Request: no valid session ID provided",
-            },
-            id: null,
-          }),
+        sendJsonRpcError(
+          res,
+          400,
+          -32000,
+          "Bad Request: no valid session ID provided",
+        );
+        return;
+      }
+      // Resolve the per-session config from the request (per-user identity) when
+      // a resolver was supplied; otherwise use the static config unchanged. The
+      // resolver may throw (e.g. bad credentials) — surface a clean 401, never
+      // a created session.
+      let sessionConfig: DocmostMcpConfig;
+      let identity: string | undefined;
+      try {
+        sessionConfig =
+          typeof config === "function" ? await config(req) : config;
+        if (options.identify) identity = await options.identify(req);
+      } catch (err) {
+        sendJsonRpcError(
+          res,
+          401,
+          -32001,
+          err instanceof Error ? err.message : "Unauthorized",
         );
         return;
       }
@@ -70,33 +138,60 @@ export function createMcpHttpHandler(config: DocmostMcpConfig) {
         onsessioninitialized: (sid: string) => {
           transports[sid] = transport!;
           lastSeen[sid] = Date.now();
+          // Bind the resolved identity to the new session id for anti-fixation.
+          if (identity !== undefined) sessionIdentity[sid] = identity;
         },
       });
       transport.onclose = () => {
         const sid = transport!.sessionId;
         if (sid && transports[sid]) delete transports[sid];
+        if (sid) delete sessionIdentity[sid];
       };
-      const server = createDocmostMcpServer(config);
+      const server = createDocmostMcpServer(sessionConfig);
       await server.connect(transport);
       await transport.handleRequest(req, res, parsedBody);
       return;
     }
 
     if (!transport) {
-      res.statusCode = 400;
-      res.setHeader("Content-Type", "application/json");
-      res.end(
-        JSON.stringify({
-          jsonrpc: "2.0",
-          error: {
-            code: -32000,
-            message: "Bad Request: no valid session ID provided",
-          },
-          id: null,
-        }),
+      sendJsonRpcError(
+        res,
+        400,
+        -32000,
+        "Bad Request: no valid session ID provided",
       );
       return;
     }
+
+    // Anti-session-fixation: a request reusing an existing session id must
+    // present credentials/token that resolve to the SAME identity bound at
+    // initialize, otherwise reject with 401. This prevents hijacking another
+    // user's established session by replaying its session id with different
+    // credentials.
+    if (options.identify && sessionId && sessionId in sessionIdentity) {
+      let presented: string;
+      try {
+        presented = await options.identify(req);
+      } catch (err) {
+        sendJsonRpcError(
+          res,
+          401,
+          -32001,
+          err instanceof Error ? err.message : "Unauthorized",
+        );
+        return;
+      }
+      if (presented !== sessionIdentity[sessionId]) {
+        sendJsonRpcError(
+          res,
+          401,
+          -32001,
+          "Credentials do not match the user that owns this MCP session.",
+        );
+        return;
+      }
+    }
+
     // Routing to an existing transport: refresh its idle timestamp.
     if (sessionId) lastSeen[sessionId] = Date.now();
     await transport.handleRequest(req, res, parsedBody);
diff --git a/packages/mcp/test/unit/http-resolver.test.mjs b/packages/mcp/test/unit/http-resolver.test.mjs
new file mode 100644
index 00000000..b3d7f39b
--- /dev/null
+++ b/packages/mcp/test/unit/http-resolver.test.mjs
@@ -0,0 +1,234 @@
+// Unit tests for createMcpHttpHandler's config-resolver + anti-fixation hook
+// (http.ts). These assert the wrapper contract WITHOUT depending on the MCP
+// SDK's full initialize handshake succeeding:
+//   - a STATIC config is still accepted (back-compat: stdio / service account)
+//     and never invokes a resolver;
+//   - a RESOLVER is accepted and is invoked exactly once on a session-init POST;
+//   - the resolver/identify path runs BEFORE the transport, so a thrown
+//     resolver error surfaces as a clean 401 and no session is created.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { Readable } from "node:stream";
+import { createMcpHttpHandler } from "../../build/http.js";
+
+// A minimal initialize JSON-RPC request body (isInitializeRequest checks
+// method === "initialize" + jsonrpc + an object params with protocolVersion).
+const INIT_BODY = {
+  jsonrpc: "2.0",
+  id: 1,
+  method: "initialize",
+  params: {
+    protocolVersion: "2025-03-26",
+    capabilities: {},
+    clientInfo: { name: "test", version: "0.0.0" },
+  },
+};
+
+// Fake Node req: a readable stream is fine; we pass parsedBody explicitly so the
+// transport never reads the stream, and our resolver short-circuits before that.
+function makeReq({ method = "POST", headers = {} } = {}) {
+  const req = new Readable({ read() {} });
+  req.method = method;
+  req.headers = headers;
+  req.push(null);
+  return req;
+}
+
+// Fake Node res capturing statusCode + body, mimicking just what http.ts uses.
+function makeRes() {
+  const chunks = [];
+  return {
+    statusCode: 200,
+    headers: {},
+    headersSent: false,
+    setHeader(k, v) {
+      this.headers[k.toLowerCase()] = v;
+    },
+    end(data) {
+      if (data) chunks.push(data);
+      this.headersSent = true;
+      this.ended = true;
+    },
+    body() {
+      return chunks.join("");
+    },
+  };
+}
+
+test("static config is accepted and never calls a resolver (back-compat)", async () => {
+  // A static config object — the stdio / service-account path. A NON-initialize
+  // POST with no session id must hit the 400 branch deterministically, proving
+  // the static handler is wired and no resolver is consulted.
+  const handler = createMcpHttpHandler({
+    apiUrl: "http://127.0.0.1:3000/api",
+    email: "svc@example.com",
+    password: "secret",
+  });
+  const req = makeReq({ method: "POST", headers: {} });
+  const res = makeRes();
+  await handler.handleRequest(req, res, { jsonrpc: "2.0", method: "ping", id: 9 });
+  assert.equal(res.statusCode, 400);
+  assert.match(res.body(), /no valid session ID/);
+});
+
+test("resolver is invoked exactly once on a session-init POST", async () => {
+  let calls = 0;
+  const handler = createMcpHttpHandler((req) => {
+    calls += 1;
+    // Throw a sentinel so we observe invocation without driving the full
+    // SDK handshake; http.ts turns a resolver throw into a clean 401.
+    throw new Error("sentinel-from-resolver");
+  });
+  const req = makeReq({ method: "POST", headers: {} });
+  const res = makeRes();
+  await handler.handleRequest(req, res, INIT_BODY);
+  assert.equal(calls, 1, "resolver must be called exactly once per init");
+  assert.equal(res.statusCode, 401);
+  assert.match(res.body(), /sentinel-from-resolver/);
+});
+
+test("resolver is NOT invoked for a non-init POST without a session id", async () => {
+  let calls = 0;
+  const handler = createMcpHttpHandler(() => {
+    calls += 1;
+    return { apiUrl: "http://127.0.0.1:3000/api", getToken: async () => "t" };
+  });
+  const req = makeReq({ method: "POST", headers: {} });
+  const res = makeRes();
+  await handler.handleRequest(req, res, { jsonrpc: "2.0", method: "ping", id: 2 });
+  assert.equal(calls, 0);
+  assert.equal(res.statusCode, 400);
+});
+
+test("identify hook throwing on init surfaces as a clean 401", async () => {
+  const handler = createMcpHttpHandler(
+    () => ({ apiUrl: "http://127.0.0.1:3000/api", getToken: async () => "t" }),
+    {
+      identify: () => {
+        throw new Error("bad-identity");
+      },
+    },
+  );
+  const req = makeReq({ method: "POST", headers: {} });
+  const res = makeRes();
+  await handler.handleRequest(req, res, INIT_BODY);
+  assert.equal(res.statusCode, 401);
+  assert.match(res.body(), /bad-identity/);
+});
+
+// Drive a REAL initialize handshake (over a loopback http server so the SDK's
+// StreamableHTTPServerTransport gets genuine Node req/res objects), capture the
+// assigned mcp-session-id, then replay subsequent requests to exercise the
+// anti-fixation identify comparison: the SAME identity is accepted (routed to
+// the transport), a DIFFERENT identity is rejected 401, and crucially the
+// per-session config RESOLVER is consulted only ONCE (at init), never on a
+// subsequent request — proving subsequent requests do not re-mint the config.
+test("subsequent request: SAME identity routes through, DIFFERENT identity is 401, resolver runs once", async () => {
+  const http = await import("node:http");
+
+  let resolverCalls = 0;
+  let currentIdentity = "user-a";
+  const handler = createMcpHttpHandler(
+    () => {
+      resolverCalls += 1;
+      return { apiUrl: "http://127.0.0.1:3000/api", getToken: async () => "t" };
+    },
+    { identify: () => currentIdentity },
+  );
+
+  // Loopback server: every request is bridged into the MCP handler with its body
+  // parsed from JSON, exactly like the embedding host does.
+  const server = http.createServer((req, res) => {
+    let raw = "";
+    req.on("data", (c) => (raw += c));
+    req.on("end", () => {
+      const body = raw ? JSON.parse(raw) : undefined;
+      handler.handleRequest(req, res, body).catch(() => {
+        if (!res.headersSent) {
+          res.statusCode = 500;
+          res.end();
+        }
+      });
+    });
+  });
+  await new Promise((r) => server.listen(0, "127.0.0.1", r));
+  const { port } = server.address();
+
+  const call = (headers, body) =>
+    new Promise((resolve) => {
+      const r = http.request(
+        {
+          host: "127.0.0.1",
+          port,
+          method: "POST",
+          path: "/mcp",
+          headers: {
+            "Content-Type": "application/json",
+            Accept: "application/json, text/event-stream",
+            ...headers,
+          },
+        },
+        (resp) => {
+          let data = "";
+          resp.on("data", (c) => (data += c));
+          resp.on("end", () =>
+            resolve({
+              statusCode: resp.statusCode,
+              sessionId: resp.headers["mcp-session-id"],
+              body: data,
+            }),
+          );
+        },
+      );
+      r.end(JSON.stringify(body));
+    });
+
+  try {
+    // 1) Establish a session via a real initialize POST (identity = user-a).
+    const init = await call({}, INIT_BODY);
+    assert.equal(resolverCalls, 1, "resolver runs exactly once at init");
+    const sid = init.sessionId;
+    assert.ok(sid, "initialize must assign an mcp-session-id");
+
+    // 2) Subsequent request, SAME identity: not a 401, resolver NOT re-run.
+    const ok = await call(
+      { "mcp-session-id": sid },
+      { jsonrpc: "2.0", method: "ping", id: 5 },
+    );
+    assert.notEqual(ok.statusCode, 401, "same identity must not be rejected");
+    assert.equal(resolverCalls, 1, "resolver is NOT re-run on a subsequent request");
+
+    // 3) Subsequent request, DIFFERENT identity: rejected 401 (anti-fixation).
+    currentIdentity = "user-b";
+    const bad = await call(
+      { "mcp-session-id": sid },
+      { jsonrpc: "2.0", method: "ping", id: 6 },
+    );
+    assert.equal(bad.statusCode, 401, "different identity hijack is rejected");
+    assert.match(bad.body, /do not match the user/);
+    assert.equal(resolverCalls, 1, "still no resolver re-run on the rejected request");
+  } finally {
+    await new Promise((r) => server.close(r));
+  }
+});
+
+test("unknown existing session id (non-init, with session header) is 400", async () => {
+  // A request carrying a session id that was never established must not consult
+  // the resolver or identify hook — it is a plain 400 (no valid session).
+  let calls = 0;
+  const handler = createMcpHttpHandler(
+    () => {
+      calls += 1;
+      return { apiUrl: "http://127.0.0.1:3000/api", getToken: async () => "t" };
+    },
+    { identify: () => "x" },
+  );
+  const req = makeReq({
+    method: "POST",
+    headers: { "mcp-session-id": "does-not-exist" },
+  });
+  const res = makeRes();
+  await handler.handleRequest(req, res, { jsonrpc: "2.0", method: "ping", id: 3 });
+  assert.equal(res.statusCode, 400);
+  assert.equal(calls, 0);
+});