Add RFC 9207 iss parameter check to MCP 2026-07-28 conformance test for AS

src/scenarios/authorization-server/auth/spec-references.ts

@@ -5,6 +5,18 @@ export const SpecReferences: { [key: string]: SpecReference } = {
     id: 'MCP-Authorization-metadata-discovery',
     url: 'https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization#authorization-server-metadata-discovery'
   },
+  MCP_AUTH_RESPONSE_VALIDATION: {
+    id: 'MCP-Authorization-response-validation',
+    url: 'https://modelcontextprotocol.io/specification/draft/basic/authorization#authorization-response-validation'
+  },
+  RFC_9207_ISS_PARAMETER: {
+    id: 'RFC-9207-iss-parameter',
+    url: 'https://www.rfc-editor.org/rfc/rfc9207.html#section-2'
+  },
+  RFC_9207_AS_METADATA: {
+    id: 'RFC-9207-authorization-server-metadata',
+    url: 'https://www.rfc-editor.org/rfc/rfc9207.html#section-2.3'
+  },
   OAUTH_2_1_AUTHORIZATION_CODE_GRANT: {
     id: 'OAUTH-2.1-authorization-code-grant',
     url: 'https://www.ietf.org/archive/id/draft-ietf-oauth-v2-1-13.html#section-4.1'

src/scenarios/authorization-server/authorization-code-grant.test.ts

@@ -100,7 +100,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -132,7 +132,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -154,7 +154,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -173,7 +173,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -197,7 +197,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -219,7 +219,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -241,7 +241,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -273,7 +273,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -305,7 +305,7 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     const checks = await scenario.run(OPTIONS, DETAILS);
 
-    expect(checks).toHaveLength(1);
+    expect(checks).toHaveLength(3);
 
     const check = checks[0];
 
@@ -426,4 +426,114 @@ describe('AuthorizationCodeGrantScenario', () => {
 
     expect(check.status).toBe('SKIPPED');
   });
+
+  describe('SEP-2468 iss parameter (2026-07-28)', () => {
+    const DETAILS_ISS_SUPPORTED = {
+      'authorization-server-metadata-endpoint': {
+        body: {
+          ...METADATA,
+          authorization_response_iss_parameter_supported: true
+        }
+      }
+    };
+
+    const statusOf = (checks: { id: string; status: string }[], id: string) =>
+      checks.find((c) => c.id === id)?.status;
+
+    beforeEach(() => {
+      mockTokenResponse({ access_token: 'access-token', token_type: 'Bearer' });
+    });
+
+    it('passes when iss is included and advertised in metadata', async () => {
+      const scenario = new AuthorizationCodeGrantScenario();
+      mockCallbackServer(
+        scenario,
+        (state) =>
+          `http://127.0.0.1:3000/callback?code=abc&state=${state}&iss=${SERVER_URL}`
+      );
+
+      const checks = await scenario.run(OPTIONS, DETAILS_ISS_SUPPORTED);
+
+      expect(statusOf(checks, 'authorization-code-grant')).toBe('SUCCESS');
+      expect(statusOf(checks, 'sep-2468-as-include-iss')).toBe('SUCCESS');
+      expect(statusOf(checks, 'sep-2468-as-advertise-iss-supported')).toBe(
+        'SUCCESS'
+      );
+      for (const c of checks.slice(1)) {
+        expect(c.source).toEqual({ introducedIn: '2026-07-28' });
+      }
+    });
+
+    it('warns when iss is omitted and skips the advertisement check', async () => {
+      const scenario = new AuthorizationCodeGrantScenario();
+      mockCallbackServer(
+        scenario,
+        (state) => `http://127.0.0.1:3000/callback?code=abc&state=${state}`
+      );
+
+      const checks = await scenario.run(OPTIONS, DETAILS_ISS_SUPPORTED);
+
+      expect(statusOf(checks, 'sep-2468-as-include-iss')).toBe('WARNING');
+      expect(statusOf(checks, 'sep-2468-as-advertise-iss-supported')).toBe(
+        'SKIPPED'
+      );
+    });
+
+    it('fails when iss is included but not advertised in metadata', async () => {
+      const scenario = new AuthorizationCodeGrantScenario();
+      mockCallbackServer(
+        scenario,
+        (state) =>
+          `http://127.0.0.1:3000/callback?code=abc&state=${state}&iss=${SERVER_URL}`
+      );
+
+      const checks = await scenario.run(OPTIONS, DETAILS);
+
+      expect(statusOf(checks, 'sep-2468-as-include-iss')).toBe('SUCCESS');
+      const advertise = checks.find(
+        (c) => c.id === 'sep-2468-as-advertise-iss-supported'
+      );
+      expect(advertise?.status).toBe('FAILURE');
+      expect(advertise?.errorMessage).toContain(
+        'authorization_response_iss_parameter_supported'
+      );
+    });
+
+    it('fails when iss is included but advertised as false', async () => {
+      const scenario = new AuthorizationCodeGrantScenario();
+      mockCallbackServer(
+        scenario,
+        (state) =>
+          `http://127.0.0.1:3000/callback?code=abc&state=${state}&iss=${SERVER_URL}`
+      );
+
+      const checks = await scenario.run(OPTIONS, {
+        'authorization-server-metadata-endpoint': {
+          body: {
+            ...METADATA,
+            authorization_response_iss_parameter_supported: false
+          }
+        }
+      });
+
+      expect(statusOf(checks, 'sep-2468-as-advertise-iss-supported')).toBe(
+        'FAILURE'
+      );
+    });
+
+    it('evaluates iss on error responses too', async () => {
+      const scenario = new AuthorizationCodeGrantScenario();
+      mockCallbackServer(
+        scenario,
+        () => 'http://127.0.0.1:3000/callback?error=access_denied'
+      );
+
+      const checks = await scenario.run(OPTIONS, DETAILS_ISS_SUPPORTED);
+
+      expect(statusOf(checks, 'authorization-code-grant')).toBe('FAILURE');
+      const includeIss = checks.find((c) => c.id === 'sep-2468-as-include-iss');
+      expect(includeIss?.status).toBe('WARNING');
+      expect(includeIss?.errorMessage).toContain('error response');
+    });
+  });
 });

src/scenarios/authorization-server/authorization-code-grant.ts

@@ -3,7 +3,8 @@
  */
 import {
   ClientScenarioForAuthorizationServer,
-  ConformanceCheck
+  ConformanceCheck,
+  DRAFT_PROTOCOL_VERSION
 } from '../../types';
 import { startCallbackServer } from '../authorization-server/auth/helpers/createCallbackServer';
 import { request } from 'undici';
@@ -58,12 +59,15 @@ export class AuthorizationCodeGrantScenario implements ClientScenarioForAuthoriz
 - HTTP response status code of token response MUST be 200 OK
 - Content-Type header of token response MUST be application/json
 - Cache-Control header of token response MUST be no-store
-- Token response MUST return a JSON response including access_token and token_type`;
+- Token response MUST return a JSON response including access_token and token_type
+- (2026-07-28+, SEP-2468) SHOULD include the iss parameter in authorization responses, including error responses
+- (2026-07-28+, SEP-2468) If the iss parameter is included, MUST set authorization_response_iss_parameter_supported to true in metadata`;
 
   async run(
     options: AuthorizationServerOptions,
     details: Record<string, unknown>
   ): Promise<ConformanceCheck[]> {
+    let issChecks: ConformanceCheck[] = [];
     try {
       if (!options.clientId) {
         return [
@@ -116,6 +120,7 @@ export class AuthorizationCodeGrantScenario implements ClientScenarioForAuthoriz
 
         const authorizationResponseUrl =
           await callback.waitForCallback(300_000);
+        issChecks = this.checkIssParameter(authorizationResponseUrl, metadata);
 
         const errors: string[] = [];
         const code = this.validateAuthorizationResponse(
@@ -134,24 +139,100 @@ export class AuthorizationCodeGrantScenario implements ClientScenarioForAuthoriz
         this.validateTokenResponse(tokenResponse, errors);
 
         if (errors.length > 0) {
-          return [this.failureCheck(errors.join(', '))];
+          return [this.failureCheck(errors.join(', ')), ...issChecks];
         }
 
         return [
           this.successCheck({
             authorizationRequest,
             authorizationResponseUrl,
             body: redactTokens(tokenResponse.body)
-          })
+          }),
+          ...issChecks
         ];
       } finally {
         callback.close();
       }
     } catch (error) {
-      return [this.failureCheck(error)];
+      return [this.failureCheck(error), ...issChecks];
     }
   }
 
+  // SEP-2468: evaluated on every authorization response, including error responses.
+  private checkIssParameter(
+    responseUrl: string,
+    metadata: Record<string, unknown>
+  ): ConformanceCheck[] {
+    const url = new URL(responseUrl);
+    const iss = url.searchParams.getAll('iss');
+    const issPresent = iss.length > 0;
+    const isErrorResponse = url.searchParams.has('error');
+    const issSupported =
+      metadata.authorization_response_iss_parameter_supported;
+    const source = { introducedIn: DRAFT_PROTOCOL_VERSION } as const;
+    const timestamp = new Date().toISOString();
+
+    const includeIss: ConformanceCheck = {
+      id: 'sep-2468-as-include-iss',
+      name: 'AuthorizationResponseIncludesIss',
+      description:
+        'Authorization server includes the iss parameter in authorization responses, including error responses',
+      status: issPresent ? 'SUCCESS' : 'WARNING',
+      source,
+      timestamp,
+      ...(issPresent
+        ? {}
+        : {
+            errorMessage: `Authorization ${isErrorResponse ? 'error ' : ''}response does not include the iss parameter`
+          }),
+      specReferences: [
+        SpecReferences.MCP_AUTH_RESPONSE_VALIDATION,
+        SpecReferences.RFC_9207_ISS_PARAMETER
+      ],
+      details: { iss, isErrorResponse }
+    };
+
+    const advertiseCheck = {
+      id: 'sep-2468-as-advertise-iss-supported',
+      name: 'AuthorizationServerAdvertisesIssSupported',
+      description:
+        'Authorization server that includes iss sets authorization_response_iss_parameter_supported to true in its metadata',
+      source,
+      timestamp,
+      specReferences: [
+        SpecReferences.MCP_AUTH_RESPONSE_VALIDATION,
+        SpecReferences.RFC_9207_AS_METADATA
+      ],
+      details: {
+        iss,
+        authorization_response_iss_parameter_supported: issSupported
+      }
+    };
+    let advertiseIss: ConformanceCheck;
+    if (!issPresent) {
+      // The MUST is conditional on the AS including iss.
+      advertiseIss = {
+        ...advertiseCheck,
+        status: 'SKIPPED',
+        errorMessage:
+          'Not applicable: authorization response does not include the iss parameter'
+      };
+    } else if (issSupported === true) {
+      advertiseIss = { ...advertiseCheck, status: 'SUCCESS' };
+    } else {
+      advertiseIss = {
+        ...advertiseCheck,
+        status: 'FAILURE',
+        errorMessage:
+          issSupported === undefined
+            ? 'Authorization response includes iss but metadata does not include "authorization_response_iss_parameter_supported"'
+            : `Authorization response includes iss but "authorization_response_iss_parameter_supported" is ${JSON.stringify(issSupported)}, expected true`
+      };
+    }
+
+    return [includeIss, advertiseIss];
+  }
+
   private buildAuthorizationRequest(
     metadata: any,
     options: AuthorizationServerOptions

src/seps/sep-2468.yaml

@@ -15,11 +15,9 @@ requirements:
   - check: sep-2468-client-no-normalization
     text: 'After decoding the iss value from the application/x-www-form-urlencoded response per RFC 9207 Section 2.4, clients MUST NOT apply scheme or host case folding, default-port elision, trailing-slash, or percent-encoding normalization (RFC 3986 Sections 6.2.2-6.2.3) before comparison.'
 
-  - text: 'MCP authorization servers SHOULD include the iss parameter in authorization responses, including error responses, as defined in RFC9207 Section 2.'
-    excluded: 'Targets the authorization server under test; observing iss in an authorization response requires driving an Authorization Code Grant against the AS, which the authorization-server suite does not implement yet (it only probes the metadata endpoint).'
-    issue: 'https://github.com/modelcontextprotocol/conformance/issues/208'
-  - text: 'Authorization servers that include the iss parameter MUST advertise this by setting authorization_response_iss_parameter_supported to true in their metadata (RFC9207 Section 2.3).'
-    excluded: 'Conditional on the AS actually including iss in an authorization response, which requires driving an Authorization Code Grant against the AS under test; the authorization-server suite does not implement that yet.'
-    issue: 'https://github.com/modelcontextprotocol/conformance/issues/208'
+  - check: sep-2468-as-include-iss
+    text: 'MCP authorization servers SHOULD include the iss parameter in authorization responses, including error responses, as defined in RFC9207 Section 2.'
+  - check: sep-2468-as-advertise-iss-supported
+    text: 'Authorization servers that include the iss parameter MUST advertise this by setting authorization_response_iss_parameter_supported to true in their metadata (RFC9207 Section 2.3).'
   - text: 'This validation applies equally to error responses - on mismatch the client MUST NOT act on or display error, error_description, or error_uri.'
     excluded: 'display is UI-facing; act-on has no protocol-observable signal beyond the existing reject-on-mismatch checks'