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Fix building auth metadata paths #779

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5577323
fix auth metadata paths
Rodriguespn May 21, 2025
521d3bc
fix lint
Rodriguespn May 22, 2025
18f88ff
more robust solution
Rodriguespn May 22, 2025
628b492
Merge branch 'modelcontextprotocol:main' into main
Rodriguespn May 23, 2025
c7068b3
refactor append_path
Rodriguespn May 23, 2025
99ef0d4
delete modify_url_path function
Rodriguespn May 25, 2025
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32 changes: 10 additions & 22 deletions src/mcp/server/auth/routes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -147,31 +147,19 @@ def create_auth_routes(
return routes


def modify_url_path(url: AnyHttpUrl, path_mapper: Callable[[str], str]) -> AnyHttpUrl:
return AnyHttpUrl.build(
scheme=url.scheme,
username=url.username,
password=url.password,
host=url.host,
port=url.port,
path=path_mapper(url.path or ""),
query=url.query,
fragment=url.fragment,
)


def build_metadata(
issuer_url: AnyHttpUrl,
service_documentation_url: AnyHttpUrl | None,
client_registration_options: ClientRegistrationOptions,
revocation_options: RevocationOptions,
) -> OAuthMetadata:
authorization_url = modify_url_path(
issuer_url, lambda path: path.rstrip("/") + AUTHORIZATION_PATH.lstrip("/")
authorization_url = AnyHttpUrl(
str(issuer_url).rstrip("/") + AUTHORIZATION_PATH
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There's no need to strip in any of those.

Suggested change
str(issuer_url).rstrip("/") + AUTHORIZATION_PATH
urljoin(str(issuer_url), AUTHORIZATION_PATH)

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Thanks for the suggestion, @Kludex!

I initially thought the same — that urljoin(str(issuer_url), "/authorize") would be enough. But it actually breaks in some cases where the base_url includes a path.

For example, when the base_url is https://example.com/auth/oidc/op/Customer/, urljoin returns https://example.com/authorize, which drops the intended path entirely. That’s because urljoin treats the /authorize as an absolute path and replaces everything after the domain.

To illustrate this, I added a test suite comparing both approaches:

import unittest
from urllib.parse import urljoin
from pydantic import AnyHttpUrl

class TestModifyUrlPath(unittest.TestCase):
    def test_append_authorize_to_urls_with_urljoin(self):
        """Test appending /authorize to various URL formats using urljoin"""
        test_cases = [
            ("https://example.com", "https://example.com/authorize"),
            ("https://example.com/", "https://example.com/authorize"),
            ("https://example.com/auth/oidc/op/Customer", "https://example.com/auth/oidc/op/Customer/authorize"),
            ("https://example.com/auth/oidc/op/Customer/", "https://example.com/auth/oidc/op/Customer/authorize"),
            ("http://localhost:8000", "http://localhost:8000/authorize"),
            ("http://localhost:8000/", "http://localhost:8000/authorize"),
        ]

        for base_url, expected in test_cases:
            any_http_url = AnyHttpUrl(base_url)
            with self.subTest(base_url=any_http_url):
                result = AnyHttpUrl(urljoin(str(any_http_url), "/authorize"))
                self.assertEqual(result, AnyHttpUrl(expected))

    def test_append_authorize_to_urls_with_rstrip(self):
        """Test appending /authorize to various URL formats using rstrip"""
        test_cases = [
            ("https://example.com", "https://example.com/authorize"),
            ("https://example.com/", "https://example.com/authorize"),
            ("https://example.com/auth/oidc/op/Customer", "https://example.com/auth/oidc/op/Customer/authorize"),
            ("https://example.com/auth/oidc/op/Customer/", "https://example.com/auth/oidc/op/Customer/authorize"),
            ("http://localhost:8000", "http://localhost:8000/authorize"),
            ("http://localhost:8000/", "http://localhost:8000/authorize"),
        ]

        for base_url, expected in test_cases:
            any_http_url = AnyHttpUrl(base_url)
            with self.subTest(base_url=any_http_url):
                result = AnyHttpUrl(str(any_http_url).rstrip("/") + "/authorize")
                self.assertEqual(result, AnyHttpUrl(expected))

if __name__ == "__main__":
    unittest.main()

So for consistency across all cases, I believe we need to keep the rstrip("/") approach.

Let me know what you think!

)
token_url = modify_url_path(
issuer_url, lambda path: path.rstrip("/") + TOKEN_PATH.lstrip("/")
token_url = AnyHttpUrl(
str(issuer_url).rstrip("/") + TOKEN_PATH
)

# Create metadata
metadata = OAuthMetadata(
issuer=issuer_url,
Expand All @@ -193,15 +181,15 @@ def build_metadata(

# Add registration endpoint if supported
if client_registration_options.enabled:
metadata.registration_endpoint = modify_url_path(
issuer_url, lambda path: path.rstrip("/") + REGISTRATION_PATH.lstrip("/")
metadata.registration_endpoint = AnyHttpUrl(
str(issuer_url).rstrip("/") + REGISTRATION_PATH
)

# Add revocation endpoint if supported
if revocation_options.enabled:
metadata.revocation_endpoint = modify_url_path(
issuer_url, lambda path: path.rstrip("/") + REVOCATION_PATH.lstrip("/")
metadata.revocation_endpoint = AnyHttpUrl(
str(issuer_url).rstrip("/") + REVOCATION_PATH
)
metadata.revocation_endpoint_auth_methods_supported = ["client_secret_post"]

return metadata
return metadata
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