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Fix substring matches in WWW-Authenticate parsing #3041

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Fix substring matches in WWW-Authenticate parsing #3041

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5de906e
Fix substring matches in WWW-Authenticate parsing
Whning0513 Jul 1, 2026
8a05814
Avoid matching auth params inside quoted values
Whning0513 Jul 1, 2026
d725212
Handle Bearer auth params in multi-challenge headers
Whning0513 Jul 2, 2026
3e99ffe
Handle more Bearer auth-param edge cases
Whning0513 Jul 6, 2026
d4cfbc5
Address WWW-Authenticate parser review feedback
Whning0513 Jul 19, 2026
b5df93c
Merge branch 'main' into fix-www-auth-substring-match-3009
Whning0513 Jul 19, 2026
397896e
Use current HTTP client name in auth tests
Whning0513 Jul 19, 2026
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4 changes: 2 additions & 2 deletions src/mcp/client/auth/utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -26,8 +26,8 @@ def extract_field_from_www_auth(response: Response, field_name: str) -> str | No
if not www_auth_header:
return None

# Pattern matches: field_name="value" or field_name=value (unquoted)
pattern = rf'{field_name}=(?:"([^"]+)"|([^\s,]+))'
# Match a complete auth-param name at the header start or after a separator.
pattern = rf'(?:^|[\s,]){re.escape(field_name)}=(?:"([^"]+)"|([^\s,]+))'
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match = re.search(pattern, www_auth_header)

if match:
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7 changes: 7 additions & 0 deletions tests/client/test_auth.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2016,6 +2016,7 @@ class TestWWWAuthenticate:
"resource_metadata",
"https://api.example.com/auth/metadata?version=1",
),
('Bearer error_scope="decoy", scope="read write"', "scope", "read write"),
],
)
def test_extract_field_from_www_auth_valid_cases(
Expand Down Expand Up @@ -2047,6 +2048,12 @@ def test_extract_field_from_www_auth_valid_cases(
# Header without requested field
('Bearer realm="api", error="insufficient_scope"', "scope", "no scope parameter"),
('Bearer realm="api", scope="read write"', "resource_metadata", "no resource_metadata parameter"),
('Bearer custom_scope="leaked"', "scope", "field name appears only as a substring"),
(
'Bearer x_resource_metadata="https://decoy.example.com"',
"resource_metadata",
"field name appears only as a substring",
),
# Malformed field (empty value)
("Bearer scope=", "scope", "malformed scope parameter"),
("Bearer resource_metadata=", "resource_metadata", "malformed resource_metadata parameter"),
Expand Down
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