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fix: discover MCP Protected Resource Metadata when server does not return 401 (#25980)

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get_protected_resource_metadata() only attempted RFC 9728 discovery when
the anonymous `initialize` probe returned 401 with a WWW-Authenticate
header. Some remote MCP servers — notably Google's Gmail/Drive/Calendar
MCPs (gmailmcp.googleapis.com, etc.) — answer 200 to an anonymous
initialize, so OAuth scope and authorization-server discovery silently
failed and connections to them could not be established.

Run the discovery regardless of the probe's HTTP status: prefer the
resource_metadata URL from WWW-Authenticate when present, and otherwise
fall back to the RFC 9728 §4.2 well-known URIs. The trade-off is a couple
of extra well-known GETs during MCP connection setup for servers that
expose no PRM document; behavior for 401-responding servers is unchanged.
This commit is contained in:
Alberto de la Cruz
2026-06-29 11:34:36 +02:00
committed by GitHub
parent f8ec63203c
commit 718b226177
1 changed files with 45 additions and 41 deletions
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86
backend/open_webui/utils/oauth.py
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@@ -372,53 +372,57 @@ async def get_protected_resource_metadata(server_url: str) -> ProtectedResourceM
headers={'Content-Type': 'application/json'},
ssl=AIOHTTP_CLIENT_SESSION_SSL,
) as response:
if response.status == 401:
resource_metadata_urls = []
match = re.search(
r'resource_metadata=(?:"([^"]+)"|([^\s,]+))',
response.headers.get('WWW-Authenticate', ''),
)
if match:
resource_metadata_urls = [match.group(1) or match.group(2)]
log.debug(f'Found resource_metadata URL: {resource_metadata_urls[0]}')
else:
# Fall back to well-known resource metadata URIs (RFC 9728 §4.2)
parsed, base_url = get_parsed_and_base_url(server_url)
if parsed.path and parsed.path != '/':
path = parsed.path.rstrip('/')
resource_metadata_urls.append(
urllib.parse.urljoin(base_url, f'/.well-known/oauth-protected-resource{path}')
)
# Discover Protected Resource Metadata regardless of HTTP status.
# A 401 carries a WWW-Authenticate header pointing at the PRM, but
# some MCP servers (e.g. Google's gmail/drive/calendar remote MCPs)
# answer 200 to an anonymous `initialize`, so we must still fall
# back to the RFC 9728 well-known URIs when there is no 401/header.
resource_metadata_urls = []
match = re.search(
r'resource_metadata=(?:"([^"]+)"|([^\s,]+))',
response.headers.get('WWW-Authenticate', ''),
)
if match:
resource_metadata_urls = [match.group(1) or match.group(2)]
log.debug(f'Found resource_metadata URL: {resource_metadata_urls[0]}')
else:
# Fall back to well-known resource metadata URIs (RFC 9728 §4.2)
parsed, base_url = get_parsed_and_base_url(server_url)
if parsed.path and parsed.path != '/':
path = parsed.path.rstrip('/')
resource_metadata_urls.append(
urllib.parse.urljoin(base_url, '/.well-known/oauth-protected-resource')
urllib.parse.urljoin(base_url, f'/.well-known/oauth-protected-resource{path}')
)
log.debug(f'No resource_metadata in header, trying well-known URIs: {resource_metadata_urls}')
resource_metadata_urls.append(
urllib.parse.urljoin(base_url, '/.well-known/oauth-protected-resource')
)
log.debug(f'No resource_metadata in header, trying well-known URIs: {resource_metadata_urls}')
# Fetch Protected Resource metadata from candidate URLs
for resource_metadata_url in resource_metadata_urls:
try:
async with session.get(
resource_metadata_url, ssl=AIOHTTP_CLIENT_SESSION_SSL
) as resource_response:
if resource_response.status == 200:
resource_metadata = await resource_response.json()
# Fetch Protected Resource metadata from candidate URLs
for resource_metadata_url in resource_metadata_urls:
try:
async with session.get(
resource_metadata_url, ssl=AIOHTTP_CLIENT_SESSION_SSL
) as resource_response:
if resource_response.status == 200:
resource_metadata = await resource_response.json()
resource = resource_metadata.get('resource') or None
if resource:
log.debug(f'Discovered resource indicator: {resource}')
resource = resource_metadata.get('resource') or None
if resource:
log.debug(f'Discovered resource indicator: {resource}')
servers = resource_metadata.get('authorization_servers', [])
scopes = resource_metadata.get('scopes_supported', [])
if scopes:
log.debug(f'Discovered resource scopes: {scopes}')
servers = resource_metadata.get('authorization_servers', [])
scopes = resource_metadata.get('scopes_supported', [])
if scopes:
log.debug(f'Discovered resource scopes: {scopes}')
if servers:
authorization_servers = servers
log.debug(f'Discovered authorization servers: {servers}')
break
except Exception as e:
log.debug(f'Failed to fetch resource metadata from {resource_metadata_url}: {e}')
continue
if servers:
authorization_servers = servers
log.debug(f'Discovered authorization servers: {servers}')
break
except Exception as e:
log.debug(f'Failed to fetch resource metadata from {resource_metadata_url}: {e}')
continue
except Exception as e:
log.debug(f'MCP Protected Resource discovery failed: {e}')