diff --git a/src/scenarios/client/auth/helpers/createAuthServer.ts b/src/scenarios/client/auth/helpers/createAuthServer.ts
index c251597..1071828 100644
--- a/src/scenarios/client/auth/helpers/createAuthServer.ts
+++ b/src/scenarios/client/auth/helpers/createAuthServer.ts
@@ -43,6 +43,11 @@ export interface AuthServerOptions {
     scope?: string;
     timestamp: string;
   }) => void;
+  onRegistrationRequest?: (req: Request) => {
+    clientId: string;
+    clientSecret?: string;
+    tokenEndpointAuthMethod?: string;
+  };
 }
 
 export function createAuthServer(
@@ -62,7 +67,8 @@ export function createAuthServer(
     clientIdMetadataDocumentSupported,
     tokenVerifier,
     onTokenRequest,
-    onAuthorizationRequest
+    onAuthorizationRequest,
+    onRegistrationRequest
   } = options;
 
   // Track scopes from the most recent authorization request
@@ -236,6 +242,17 @@ export function createAuthServer(
   });
 
   app.post(authRoutes.registration_endpoint, (req: Request, res: Response) => {
+    let clientId = 'test-client-id';
+    let clientSecret: string | undefined = 'test-client-secret';
+    let tokenEndpointAuthMethod: string | undefined;
+
+    if (onRegistrationRequest) {
+      const result = onRegistrationRequest(req);
+      clientId = result.clientId;
+      clientSecret = result.clientSecret;
+      tokenEndpointAuthMethod = result.tokenEndpointAuthMethod;
+    }
+
     checks.push({
       id: 'client-registration',
       name: 'ClientRegistration',
@@ -245,15 +262,19 @@ export function createAuthServer(
       specReferences: [SpecReferences.MCP_DCR],
       details: {
         endpoint: '/register',
-        clientName: req.body.client_name
+        clientName: req.body.client_name,
+        ...(tokenEndpointAuthMethod && { tokenEndpointAuthMethod })
       }
     });
 
     res.status(201).json({
-      client_id: 'test-client-id',
-      client_secret: 'test-client-secret',
+      client_id: clientId,
+      ...(clientSecret && { client_secret: clientSecret }),
       client_name: req.body.client_name || 'test-client',
-      redirect_uris: req.body.redirect_uris || []
+      redirect_uris: req.body.redirect_uris || [],
+      ...(tokenEndpointAuthMethod && {
+        token_endpoint_auth_method: tokenEndpointAuthMethod
+      })
     });
   });
 
diff --git a/src/scenarios/client/auth/index.ts b/src/scenarios/client/auth/index.ts
index 170c1cd..6a3ad1c 100644
--- a/src/scenarios/client/auth/index.ts
+++ b/src/scenarios/client/auth/index.ts
@@ -12,6 +12,11 @@ import {
   ScopeStepUpAuthScenario,
   ScopeRetryLimitScenario
 } from './scope-handling';
+import {
+  ClientSecretBasicAuthScenario,
+  ClientSecretPostAuthScenario,
+  PublicClientAuthScenario
+} from './token-endpoint-auth';
 import {
   ClientCredentialsJwtScenario,
   ClientCredentialsBasicScenario
@@ -27,6 +32,9 @@ export const authScenariosList: Scenario[] = [
   new ScopeOmittedWhenUndefinedScenario(),
   new ScopeStepUpAuthScenario(),
   new ScopeRetryLimitScenario(),
+  new ClientSecretBasicAuthScenario(),
+  new ClientSecretPostAuthScenario(),
+  new PublicClientAuthScenario(),
   new ClientCredentialsJwtScenario(),
   new ClientCredentialsBasicScenario()
 ];
diff --git a/src/scenarios/client/auth/token-endpoint-auth.ts b/src/scenarios/client/auth/token-endpoint-auth.ts
new file mode 100644
index 0000000..976f69b
--- /dev/null
+++ b/src/scenarios/client/auth/token-endpoint-auth.ts
@@ -0,0 +1,176 @@
+import type { Scenario, ConformanceCheck } from '../../../types.js';
+import { ScenarioUrls } from '../../../types.js';
+import { createAuthServer } from './helpers/createAuthServer.js';
+import { createServer } from './helpers/createServer.js';
+import { ServerLifecycle } from './helpers/serverLifecycle.js';
+import { SpecReferences } from './spec-references.js';
+import { MockTokenVerifier } from './helpers/mockTokenVerifier.js';
+
+type AuthMethod = 'client_secret_basic' | 'client_secret_post' | 'none';
+
+function detectAuthMethod(
+  authorizationHeader?: string,
+  bodyClientSecret?: string
+): AuthMethod {
+  if (authorizationHeader?.startsWith('Basic ')) {
+    return 'client_secret_basic';
+  }
+  if (bodyClientSecret) {
+    return 'client_secret_post';
+  }
+  return 'none';
+}
+
+function validateBasicAuthFormat(authorizationHeader: string): {
+  valid: boolean;
+  error?: string;
+} {
+  const encoded = authorizationHeader.substring('Basic '.length);
+  try {
+    const decoded = Buffer.from(encoded, 'base64').toString('utf-8');
+    if (!decoded.includes(':')) {
+      return { valid: false, error: 'missing colon separator' };
+    }
+    return { valid: true };
+  } catch {
+    return { valid: false, error: 'base64 decoding failed' };
+  }
+}
+
+const AUTH_METHOD_NAMES: Record<AuthMethod, string> = {
+  client_secret_basic: 'HTTP Basic authentication (client_secret_basic)',
+  client_secret_post: 'client_secret_post',
+  none: 'no authentication (public client)'
+};
+
+class TokenEndpointAuthScenario implements Scenario {
+  name: string;
+  description: string;
+  private expectedAuthMethod: AuthMethod;
+  private authServer = new ServerLifecycle();
+  private server = new ServerLifecycle();
+  private checks: ConformanceCheck[] = [];
+
+  constructor(expectedAuthMethod: AuthMethod) {
+    this.expectedAuthMethod = expectedAuthMethod;
+    this.name = `auth/token-endpoint-auth-${expectedAuthMethod === 'client_secret_basic' ? 'basic' : expectedAuthMethod === 'client_secret_post' ? 'post' : 'none'}`;
+    this.description = `Tests that client uses ${AUTH_METHOD_NAMES[expectedAuthMethod]} when server only supports ${expectedAuthMethod}`;
+  }
+
+  async start(): Promise<ScenarioUrls> {
+    this.checks = [];
+    const tokenVerifier = new MockTokenVerifier(this.checks, []);
+
+    const authApp = createAuthServer(this.checks, this.authServer.getUrl, {
+      tokenVerifier,
+      tokenEndpointAuthMethodsSupported: [this.expectedAuthMethod],
+      onTokenRequest: (req, timestamp) => {
+        const authorizationHeader = req.headers.authorization as
+          | string
+          | undefined;
+        const bodyClientSecret = req.body.client_secret;
+        const actualMethod = detectAuthMethod(
+          authorizationHeader,
+          bodyClientSecret
+        );
+        const isCorrect = actualMethod === this.expectedAuthMethod;
+
+        // For basic auth, also validate the format
+        let formatError: string | undefined;
+        if (actualMethod === 'client_secret_basic' && authorizationHeader) {
+          const validation = validateBasicAuthFormat(authorizationHeader);
+          if (!validation.valid) {
+            formatError = validation.error;
+          }
+        }
+
+        const status = isCorrect && !formatError ? 'SUCCESS' : 'FAILURE';
+        let description: string;
+
+        if (formatError) {
+          description = `Client sent Basic auth header but ${formatError}`;
+        } else if (isCorrect) {
+          description = `Client correctly used ${AUTH_METHOD_NAMES[this.expectedAuthMethod]} for token endpoint`;
+        } else {
+          description = `Client used ${actualMethod} but server only supports ${this.expectedAuthMethod}`;
+        }
+
+        this.checks.push({
+          id: 'token-endpoint-auth-method',
+          name: 'Token endpoint authentication method',
+          description,
+          status,
+          timestamp,
+          specReferences: [SpecReferences.OAUTH_2_1_TOKEN],
+          details: {
+            expectedAuthMethod: this.expectedAuthMethod,
+            actualAuthMethod: actualMethod,
+            hasAuthorizationHeader: !!authorizationHeader,
+            hasBodyClientSecret: !!bodyClientSecret,
+            ...(formatError && { formatError })
+          }
+        });
+      },
+      onRegistrationRequest: () => ({
+        clientId: `test-client-${Date.now()}`,
+        clientSecret:
+          this.expectedAuthMethod === 'none'
+            ? undefined
+            : `test-secret-${Date.now()}`,
+        tokenEndpointAuthMethod: this.expectedAuthMethod
+      })
+    });
+    await this.authServer.start(authApp);
+
+    const app = createServer(
+      this.checks,
+      this.server.getUrl,
+      this.authServer.getUrl,
+      {
+        prmPath: '/.well-known/oauth-protected-resource/mcp',
+        requiredScopes: [],
+        tokenVerifier
+      }
+    );
+    await this.server.start(app);
+
+    return { serverUrl: `${this.server.getUrl()}/mcp` };
+  }
+
+  async stop() {
+    await this.authServer.stop();
+    await this.server.stop();
+  }
+
+  getChecks(): ConformanceCheck[] {
+    if (!this.checks.some((c) => c.id === 'token-endpoint-auth-method')) {
+      this.checks.push({
+        id: 'token-endpoint-auth-method',
+        name: 'Token endpoint authentication method',
+        description: 'Client did not make a token request',
+        status: 'FAILURE',
+        timestamp: new Date().toISOString(),
+        specReferences: [SpecReferences.OAUTH_2_1_TOKEN]
+      });
+    }
+    return this.checks;
+  }
+}
+
+export class ClientSecretBasicAuthScenario extends TokenEndpointAuthScenario {
+  constructor() {
+    super('client_secret_basic');
+  }
+}
+
+export class ClientSecretPostAuthScenario extends TokenEndpointAuthScenario {
+  constructor() {
+    super('client_secret_post');
+  }
+}
+
+export class PublicClientAuthScenario extends TokenEndpointAuthScenario {
+  constructor() {
+    super('none');
+  }
+}