diff --git a/README.md b/README.md
index 339e205..c2c1b63 100644
--- a/README.md
+++ b/README.md
@@ -536,6 +536,14 @@ curl -X POST http://localhost:4100/user_management/authenticate \
 
 The resulting session records the method that was gated (`password`), not the verification step. Driving the grant with `user_id` instead of a pending token still works, and that session reports `unknown` — there is no primary method to recover. Fixtures that sign in with a password want `email_verified: true`, in a seed file or on `POST /user_management/users`.
 
+### SSO logins produce a session
+
+A code from `GET /sso/authorize` redeems at `POST /user_management/authenticate` with `grant_type=authorization_code`, so an app that sends people straight to their IdP with `sso.getAuthorizationUrl` and finishes at AuthKit's callback gets a real session — one whose `auth_method` is `sso`, so authorization code that hides password management for federated users can be exercised. `POST /sso/token` still redeems the same code for a bare profile and access token, which is the standalone SSO product and creates no session; a code is spent by whichever endpoint gets it first.
+
+The session is scoped to the connection's organization. A profile with no user-management account yet gets one, verified — the IdP asserted the address — the way AuthKit provisions on a first SSO login.
+
+As with `/user_management/authorize`, `/sso/authorize` is public and signs in whoever `login_hint` names: there is no IdP here to prove an identity with, and inventing a profile for any address is what lets a test drive an SSO login at all. Both endpoints will therefore hand out a session for any account you ask them for. That is the emulator being a test double, not an authorization server — do not point anything at it that you would not also let sign in as your users.
+
 ### Refresh tokens always rotate
 
 The emulator issues a new refresh token on every refresh and invalidates the one you presented, so replaying it returns `{"error": "invalid_grant", "error_description": "Invalid refresh token."}`. WorkOS documents that refresh tokens _may_ be rotated after use, so production is free to hand back the same token and leave it valid. The emulator always takes the stricter path: a client that forgets to store the newly returned `refresh_token` fails locally instead of in production.
diff --git a/src/workos/routes/auth.ts b/src/workos/routes/auth.ts
index fb3797b..477caff 100644
--- a/src/workos/routes/auth.ts
+++ b/src/workos/routes/auth.ts
@@ -31,7 +31,7 @@ import {
 } from '../helpers.js';
 import { renderConfiguredJwtTemplate } from '../jwt-template.js';
 import type { EventBus } from '../event-bus.js';
-import type { WorkOSInvitation } from '../entities.js';
+import type { WorkOSInvitation, WorkOSSSOAuthorization, WorkOSUser } from '../entities.js';
 import { STORE_KEYS, STORE_KEY_PREFIXES } from '../constants.js';
 import { renderLoginPage, renderDeviceVerifyPage } from '../login-page.js';
 
@@ -257,7 +257,12 @@ export function authRoutes(ctx: RouteContext): void {
     /** Emit the spec's authentication.*_failed event for a credential failure, then throw. */
     const failAuth: (
       method: string,
-      info: { email?: string | null; userId?: string | null },
+      info: {
+        email?: string | null;
+        userId?: string | null;
+        /** Required on every authentication.sso_* event, per the spec's event data. */
+        sso?: { organization_id: string | null; connection_id: string | null; session_id: string | null };
+      },
       error: WorkOSApiError,
     ) => never = (method, info, error) => {
       emitAuthenticationEvent({
@@ -269,10 +274,83 @@ export function authRoutes(ctx: RouteContext): void {
         ipAddress: requestIp,
         userAgent: requestUserAgent,
         error: { code: error.code, message: error.message },
+        sso: info.sso,
       });
       throw error;
     };
 
+    /**
+     * Redeem an /sso/authorize code into the user-management user it signs in, provisioning one
+     * when the federated profile has no account yet — AuthKit does the same on a first SSO login,
+     * and /sso/authorize mints a profile for any address it is handed, so refusing here would
+     * report a code the emulator had just issued as invalid.
+     *
+     * Provisioning deliberately lands before the shared template gate below: a JWT template that
+     * cannot render fails the request but keeps the user, the same way the gate already keeps the
+     * membership acceptInvitation persists. Both are real domain progress — the user is the exact
+     * record a successful retry would create — and the burned code matches what a template failure
+     * costs every other one-time grant.
+     */
+    const redeemSsoAuthorization = (ssoAuth: WorkOSSSOAuthorization, code: string): WorkOSUser => {
+      const profile = ws.ssoProfiles.get(ssoAuth.profile_id);
+
+      if (isExpired(ssoAuth.expires_at)) {
+        ws.ssoAuthorizations.delete(ssoAuth.id);
+        failAuth(
+          'SSO',
+          {
+            email: profile?.email,
+            userId: findUserByEmail(ws, profile?.email ?? '')?.id ?? null,
+            sso: {
+              organization_id: ssoAuth.organization_id,
+              connection_id: ssoAuth.connection_id,
+              session_id: null,
+            },
+          },
+          new OauthApiError(400, 'invalid_grant', `The code '${code}' has expired or is invalid.`),
+        );
+      }
+
+      // The same emulator-state failure /sso/token names, for the same reason: an authorization
+      // pointing at a profile that no longer exists is not a request anyone can fix by sending
+      // something else, so it stays plain rather than OAuth-shaped.
+      if (!profile) throw new WorkOSApiError(500, 'Profile not found', 'server_error');
+
+      // The shared recipient check below runs only after the grant, and by then this helper has
+      // spent the one-time authorization and possibly provisioned an account — a mismatched
+      // invitation would fail the request yet leave a user behind with no session. The profile
+      // already names who is signing in, so ask before anything is consumed; a rejected caller
+      // keeps the code and retries without the invitation.
+      if (invitation && !emailsMatch(invitation.email, profile.email)) {
+        throw new WorkOSApiError(
+          400,
+          'The invitation was issued for a different email address',
+          'invitation_cannot_be_used_for_email',
+        );
+      }
+
+      ws.ssoAuthorizations.delete(ssoAuth.id);
+
+      const existing = findUserByEmail(ws, profile.email);
+      if (existing) return existing;
+      return ws.users.insert({
+        object: 'user',
+        email: profile.email,
+        name: null,
+        first_name: profile.first_name,
+        last_name: profile.last_name,
+        // The IdP asserted the address, which is what verification proves.
+        email_verified: true,
+        profile_picture_url: null,
+        last_sign_in_at: null,
+        external_id: null,
+        metadata: {},
+        locale: null,
+        password_hash: null,
+        impersonator: null,
+      });
+    };
+
     /**
      * Initiate the MFA second factor. Records the primary method on a pending-auth token so
      * the eventual session reports it (not 'unknown'), creates a challenge for the factor, and
@@ -371,6 +449,9 @@ export function authRoutes(ctx: RouteContext): void {
     // a leniency production doesn't permit — store null. In both cases the redemption request
     // is the only client identity the emulator ever has.
     let grantClientId: string | undefined;
+    // The connection an SSO sign-in came through, carried to the authentication.sso_succeeded
+    // event, whose spec payload requires an `sso` block. Null for every other grant.
+    let ssoContext: { organization_id: string | null; connection_id: string | null } | null = null;
 
     switch (grantType) {
       case 'authorization_code': {
@@ -381,6 +462,23 @@ export function authRoutes(ctx: RouteContext): void {
         // as invalid_grant with the same description.
         const authCode = ws.authCodes.findOneBy('code', code);
         if (!authCode) {
+          // A code minted by /sso/authorize is redeemable here too. The two endpoints wrote to
+          // different stores, so an app that starts SSO with `sso.getAuthorizationUrl` — sending
+          // people straight to their IdP rather than through a hosted screen — and finishes at
+          // AuthKit's callback got invalid_grant for a code the emulator had just issued.
+          // /sso/token still redeems the same code for a bare profile; this is the path that
+          // produces a session, and the only one that records auth_method 'sso'.
+          const ssoAuth = ws.ssoAuthorizations.findOneBy('code', code);
+          if (ssoAuth) {
+            user = redeemSsoAuthorization(ssoAuth, code);
+            organizationId = ssoAuth.organization_id;
+            ssoContext = { organization_id: ssoAuth.organization_id, connection_id: ssoAuth.connection_id };
+            // An SSO authorization records no client_id, so the redeeming request is the only
+            // client identity there is — the same fallback a client-less /authorize gets.
+            grantClientId = clientId;
+            authMethod = 'SSO';
+            break;
+          }
           failAuth(
             'OAuth',
             {},
@@ -988,6 +1086,9 @@ export function authRoutes(ctx: RouteContext): void {
         email: updatedUser.email,
         ipAddress: session.ip_address,
         userAgent: session.user_agent,
+        // Required on authentication.sso_* by the spec's event data. This is the only SSO path
+        // that reaches a session, so it is also the only one that can report a session_id.
+        sso: ssoContext ? { ...ssoContext, session_id: session.id } : undefined,
       });
     }
 
diff --git a/src/workos/routes/sso.spec.ts b/src/workos/routes/sso.spec.ts
index 6c0c306..f46caa3 100644
--- a/src/workos/routes/sso.spec.ts
+++ b/src/workos/routes/sso.spec.ts
@@ -107,6 +107,121 @@ describe('SSO routes', () => {
     expect(new Set(profiles.map((p) => p.connection_id))).toEqual(new Set([conn.id, conn2.id]));
   });
 
+  describe('SSO code redeemed for a user-management session', () => {
+    /** Start SSO through `conn` and return the code the redirect carries. */
+    async function ssoCode(connId: string, loginHint?: string) {
+      const res = await app.request(
+        `/sso/authorize?connection=${connId}&redirect_uri=http://localhost:3000/callback` +
+          (loginHint ? `&login_hint=${encodeURIComponent(loginHint)}` : ''),
+      );
+      return new URL(res.headers.get('location')!).searchParams.get('code')!;
+    }
+
+    const authenticate = (code: string, extra?: Record<string, unknown>) =>
+      app.request('/user_management/authenticate', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ grant_type: 'authorization_code', code, client_id: 'client_x', ...extra }),
+      });
+
+    it('signs the profile in, keying the session to sso', async () => {
+      const { org, conn } = await createOrgWithConnection();
+      const ws = getWorkOSStore(store);
+      const user = ws.users.insert({
+        object: 'user',
+        email: 'alice@sso.example.com',
+        name: null,
+        first_name: null,
+        last_name: null,
+        email_verified: true,
+        profile_picture_url: null,
+        last_sign_in_at: null,
+        external_id: null,
+        metadata: {},
+        locale: null,
+        password_hash: null,
+        impersonator: null,
+      });
+
+      const res = await authenticate(await ssoCode(conn.id, 'alice@sso.example.com'));
+
+      expect(res.status).toBe(200);
+      const body = await json(res);
+      expect(body.user.id).toBe(user.id);
+      expect(body.organization_id).toBe(org.id);
+      expect(body.authentication_method).toBe('SSO');
+      const [session] = ws.sessions.findBy('user_id', user.id);
+      expect(session.auth_method).toBe('sso');
+
+      // The spec requires an `sso` block on authentication.sso_succeeded; this is the only SSO
+      // path that reaches a session, so it is the only one that can fill in session_id.
+      const [event] = ws.events.all().filter((e) => e.event === 'authentication.sso_succeeded');
+      expect(event.data).toMatchObject({
+        type: 'sso',
+        status: 'succeeded',
+        user_id: user.id,
+        sso: { organization_id: org.id, connection_id: conn.id, session_id: session.id },
+      });
+    });
+
+    it('provisions a user the federated profile has no account for', async () => {
+      const { conn } = await createOrgWithConnection();
+
+      const body = await json(await authenticate(await ssoCode(conn.id, 'newcomer@sso.example.com')));
+
+      expect(body.user.email).toBe('newcomer@sso.example.com');
+      // The IdP asserted the address, which is what verification proves.
+      expect(body.user.email_verified).toBe(true);
+      expect(getWorkOSStore(store).users.all()).toHaveLength(1);
+    });
+
+    it('spends the code once, and reports an expired one as invalid_grant', async () => {
+      const { org, conn } = await createOrgWithConnection();
+      const ws = getWorkOSStore(store);
+
+      const code = await ssoCode(conn.id, 'once@sso.example.com');
+      expect((await authenticate(code)).status).toBe(200);
+      const replay = await authenticate(code);
+      expect(replay.status).toBe(400);
+      expect((await json(replay)).error).toBe('invalid_grant');
+
+      const expired = await ssoCode(conn.id, 'stale@sso.example.com');
+      const stored = ws.ssoAuthorizations.findOneBy('code', expired)!;
+      ws.ssoAuthorizations.update(stored.id, { expires_at: new Date(Date.now() - 1000).toISOString() });
+
+      const res = await authenticate(expired);
+      expect(res.status).toBe(400);
+      expect((await json(res)).error).toBe('invalid_grant');
+      const [failed] = ws.events.all().filter((e) => e.event === 'authentication.sso_failed');
+      expect(failed.data).toMatchObject({
+        type: 'sso',
+        status: 'failed',
+        email: 'stale@sso.example.com',
+        sso: { organization_id: org.id, connection_id: conn.id, session_id: null },
+      });
+    });
+
+    it('rejects a mismatched invitation before the code is spent or a user provisioned', async () => {
+      const { org, conn } = await createOrgWithConnection();
+      const invitation = await json(
+        await req('/user_management/invitations', {
+          method: 'POST',
+          body: JSON.stringify({ email: 'recipient@sso.example.com', organization_id: org.id }),
+        }),
+      );
+
+      const code = await ssoCode(conn.id, 'interloper@sso.example.com');
+      const res = await authenticate(code, { invitation_token: invitation.token });
+
+      expect(res.status).toBe(400);
+      expect((await json(res)).code).toBe('invitation_cannot_be_used_for_email');
+      // Nothing was consumed: no account was provisioned for the interloper, and the same code
+      // still signs in once the invitation is dropped.
+      expect(getWorkOSStore(store).users.all()).toHaveLength(0);
+      expect((await authenticate(code)).status).toBe(200);
+    });
+  });
+
   it('sso token exchange returns profile and access_token', async () => {
     const { conn } = await createOrgWithConnection();