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fix: preserve exact OAuth resource indicators (#2581)

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Co-authored-by: Konstantin Konstantinov <konstantin@mach5technology.com>
This commit is contained in:
Hugo Moreira 2026-09-03 09:36:13 -07:00 • committed by GitHub
commit 5119ee7fd7
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3 changed files with 120 additions and 11 deletions
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5
.changeset/plenty-plums-sip.md Normal file
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@ -0,0 +1,5 @@
---
'@modelcontextprotocol/client': patch
---
Preserve the exact OAuth resource indicator from protected resource metadata when building authorization and token requests. Previously a pathless `resource` such as `https://example.com` was normalized to `https://example.com/` via `URL.href`, which breaks authorization servers that require the `resource` parameter to match the published value exactly (Microsoft Entra ID rejects it with `AADSTS9010010`). The exported OAuth helpers (`startAuthorization`, `exchangeAuthorization`, `refreshAuthorization`, `fetchToken`, `executeTokenRequest`) now also accept a `string` for `resource`; `selectResourceURL` still returns a `URL`, and a provider's `validateResourceURL` result is used unchanged. Fixes #1968.

39
packages/client/src/client/auth.ts
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@ -1243,11 +1243,17 @@ async function authInternal(
await provider.saveDiscoveryState?.(freshDiscoveryState);
}
const resource: URL | undefined = await selectResourceURL(serverUrl, provider, resourceMetadata);
// Send the metadata's resource indicator verbatim: `selectResourceURL` returns a parsed
// `URL`, and `URL.href` appends "/" to a pathless indicator such as `https://example.com`,
// which exact-match authorization servers reject (#1968). A URL returned by the
// provider's own `validateResourceURL` is used as returned.
const selectedResource = await selectResourceURL(serverUrl, provider, resourceMetadata);
const resource: string | URL | undefined =
selectedResource && resourceMetadata && !provider.validateResourceURL ? resourceMetadata.resource : selectedResource;
// Save resource URL for providers that need it (e.g., CrossAppAccessProvider)
if (resource) {
await provider.saveResourceUrl?.(String(resource));
await provider.saveResourceUrl?.(resourceIndicatorToString(resource));
}
// Scope selection used consistently for DCR and the authorization request.
@ -1460,6 +1466,17 @@ export function isHttpsUrl(value?: string): boolean {
}
}
/**
* Selects the RFC 8707 resource indicator for an MCP server: the provider's
* {@linkcode OAuthClientProvider.validateResourceURL | validateResourceURL} result when
* implemented, otherwise the protected resource metadata's `resource` (checked against the
* server URL with `checkResourceAllowed`), or `undefined` when there is no metadata.
*
* The result is a parsed `URL`, so a pathless indicator such as `https://example.com` has
* the `href` `https://example.com/`. {@linkcode auth} therefore sends the metadata string
* verbatim instead of this URL's `href` (#1968); callers that emit the `resource`
* parameter themselves should do the same.
*/
export async function selectResourceURL(
serverUrl: string | URL,
provider: OAuthClientProvider,
@ -2032,6 +2049,10 @@ export async function discoverOAuthServerInfo(
};
}
function resourceIndicatorToString(resource: string | URL): string {
return typeof resource === 'string' ? resource : resource.href;
}
/**
* Begins the authorization flow with the given server, by generating a PKCE challenge and constructing the authorization URL.
*/
@ -2050,7 +2071,7 @@ export async function startAuthorization(
redirectUrl: string | URL;
scope?: string;
state?: string;
resource?: URL;
resource?: string | URL;
}
): Promise<{ authorizationUrl: URL; codeVerifier: string }> {
let authorizationUrl: URL;
@ -2098,7 +2119,7 @@ export async function startAuthorization(
}
if (resource) {
authorizationUrl.searchParams.set('resource', resource.href);
authorizationUrl.searchParams.set('resource', resourceIndicatorToString(resource));
}
return { authorizationUrl, codeVerifier };
@ -2147,7 +2168,7 @@ export async function executeTokenRequest(
tokenRequestParams: URLSearchParams;
clientInformation?: OAuthClientInformationMixed;
addClientAuthentication?: OAuthClientProvider['addClientAuthentication'];
resource?: URL;
resource?: string | URL;
/**
* SEP-1932 / RFC 9449 §5: when set, signs a DPoP proof into the token request's `DPoP`
* header — the prerequisite for obtaining a DPoP-bound access token. On a `400
@ -2166,7 +2187,7 @@ export async function executeTokenRequest(
});
if (resource) {
tokenRequestParams.set('resource', resource.href);
tokenRequestParams.set('resource', resourceIndicatorToString(resource));
}
if (!addClientAuthentication && clientInformation) {
@ -2269,7 +2290,7 @@ export async function exchangeAuthorization(
iss?: string;
codeVerifier: string;
redirectUri: string | URL;
resource?: URL;
resource?: string | URL;
addClientAuthentication?: OAuthClientProvider['addClientAuthentication'];
/** SEP-1932 / RFC 9449: see {@linkcode executeTokenRequest}'s `dpop` option. */
dpop?: DpopSession;
@ -2321,7 +2342,7 @@ export async function refreshAuthorization(
metadata?: AuthorizationServerMetadata;
clientInformation: OAuthClientInformationMixed;
refreshToken: string;
resource?: URL;
resource?: string | URL;
addClientAuthentication?: OAuthClientProvider['addClientAuthentication'];
/** SEP-1932 / RFC 9449: see {@linkcode executeTokenRequest}'s `dpop` option. */
dpop?: DpopSession;
@ -2386,7 +2407,7 @@ export async function fetchToken(
fetchFn
}: {
metadata?: AuthorizationServerMetadata;
resource?: URL;
resource?: string | URL;
/** Authorization code for the default `authorization_code` grant flow */
authorizationCode?: string;
/**

87
packages/client/test/client/auth.test.ts
View file

@ -1496,7 +1496,8 @@ describe('OAuth Authorization', () => {
it('calls saveDiscoveryState after discovery when provider implements it', async () => {
const saveDiscoveryState = vi.fn();
const provider = createMockProvider({ saveDiscoveryState });
const saveResourceUrl = vi.fn();
const provider = createMockProvider({ saveDiscoveryState, saveResourceUrl });
mockFetch.mockImplementation(url => {
const urlString = url.toString();
@ -1529,6 +1530,9 @@ describe('OAuth Authorization', () => {
authorizationServerMetadata: validAuthMetadata
})
);
expect(saveResourceUrl).toHaveBeenCalledWith('https://resource.example.com');
const authorizationUrl = vi.mocked(provider.redirectToAuthorization).mock.calls[0]![0];
expect(authorizationUrl.searchParams.get('resource')).toBe('https://resource.example.com');
});
it('restores full discovery state from cache including resource metadata', async () => {
@ -1580,7 +1584,7 @@ describe('OAuth Authorization', () => {
const tokenCall = mockFetch.mock.calls.find(call => call[0].toString().includes('/token'));
expect(tokenCall).toBeDefined();
const body = tokenCall![1].body as URLSearchParams;
expect(body.get('resource')).toBe('https://resource.example.com/');
expect(body.get('resource')).toBe('https://resource.example.com');
});
it('re-saves enriched state when partial cache is supplemented with fetched metadata', async () => {
@ -1787,6 +1791,16 @@ describe('OAuth Authorization', () => {
expect(codeVerifier).toBe('test_verifier');
});
it('preserves a string resource indicator without URL normalization', async () => {
const { authorizationUrl } = await startAuthorization('https://auth.example.com', {
clientInformation: validClientInfo,
redirectUrl: 'http://localhost:3000/callback',
resource: 'https://api.example.com'
});
expect(authorizationUrl.searchParams.get('resource')).toBe('https://api.example.com');
});
it('includes scope parameter when provided', async () => {
const { authorizationUrl } = await startAuthorization('https://auth.example.com', {
clientInformation: validClientInfo,
@ -3353,6 +3367,75 @@ describe('OAuth Authorization', () => {
expect(authUrl.searchParams.get('resource')).toBe('https://api.example.com/');
});
it('sends a pathless PRM resource verbatim on the authorization and token requests (#1968)', async () => {
// RFC 9728 publishes the resource identifier and RFC 8707 requires it to be
// sent unchanged. `new URL('https://example.com').href` is 'https://example.com/',
// and authorization servers that match the indicator exactly (Microsoft Entra
// ID: AADSTS9010010) reject the extra slash.
mockFetch.mockImplementation(url => {
const urlString = url.toString();
if (urlString.includes('/.well-known/oauth-protected-resource')) {
return Promise.resolve({
ok: true,
status: 200,
json: async () => ({
resource: 'https://example.com',
authorization_servers: ['https://auth.example.com'],
scopes_supported: ['https://example.com/mcp:tools']
})
});
} else if (urlString.includes('/.well-known/oauth-authorization-server')) {
return Promise.resolve({
ok: true,
status: 200,
json: async () => ({
issuer: 'https://auth.example.com',
authorization_endpoint: 'https://auth.example.com/authorize',
token_endpoint: 'https://auth.example.com/token',
response_types_supported: ['code'],
code_challenge_methods_supported: ['S256']
})
});
} else if (urlString.includes('/token')) {
return Promise.resolve({
ok: true,
status: 200,
json: async () => ({ access_token: 'access123', token_type: 'bearer', expires_in: 3600 })
});
}
return Promise.resolve({ ok: false, status: 404 });
});
(mockProvider.clientInformation as Mock).mockResolvedValue({
client_id: 'test-client',
client_secret: 'test-secret'
});
(mockProvider.tokens as Mock).mockResolvedValue(undefined);
(mockProvider.saveCodeVerifier as Mock).mockResolvedValue(undefined);
(mockProvider.redirectToAuthorization as Mock).mockResolvedValue(undefined);
(mockProvider.codeVerifier as Mock).mockResolvedValue('verifier123');
(mockProvider.saveTokens as Mock).mockResolvedValue(undefined);
// Authorization request: the redirect carries the metadata value byte for byte.
const redirectResult = await auth(mockProvider, { serverUrl: 'https://example.com/mcp' });
expect(redirectResult).toBe('REDIRECT');
const authUrl: URL = (mockProvider.redirectToAuthorization as Mock).mock.calls[0]![0];
expect(authUrl.searchParams.get('resource')).toBe('https://example.com');
// Token request: the authorization-code exchange sends the same value.
const exchangeResult = await auth(mockProvider, {
serverUrl: 'https://example.com/mcp',
authorizationCode: 'code123'
});
expect(exchangeResult).toBe('AUTHORIZED');
const tokenCall = mockFetch.mock.calls.find(call => call[0].toString().includes('/token'));
expect(tokenCall).toBeDefined();
const body = tokenCall![1].body as URLSearchParams;
expect(body.get('resource')).toBe('https://example.com');
});
it('excludes resource parameter when Protected Resource Metadata is not present', async () => {
// Mock metadata discovery where protected resource metadata is not available (404)
// but authorization server metadata is available