DefaultBearerTokenResolver rejects RFC-legal multi-space `Authorization` header

Component: spring-security-oauth2-resource-server · Affects: 6.5.x, 7.1.0, current main

Problem

DefaultBearerTokenResolver matches the header against
^Bearer (?<token>[a-zA-Z0-9-._~+/]+=*)$ — a single literal space. RFC 6750 §2.1
(credentials = "Bearer" 1*SP b64token) and RFC 9110 §11.6.2 (1*SP) allow one or more
spaces. A conformant Authorization: Bearer␣␣<token> is therefore rejected with
invalid_token / "Bearer token is malformed".

Reproduce

Send an otherwise valid request with two spaces after Bearer:

Authorization: Bearer  eyJhbGciOi...

→ HTTP 401, WWW-Authenticate: Bearer error="invalid_token", error_description="Bearer token is malformed".

The token never reaches the decoder; it fails at header resolution.

Expected

Per 1*SP, the token is resolved and validated normally (→ 200 for a valid token).

Notes

• Masked by some servlet containers: Undertow (2.3.24) collapses the double space to one so
  Spring accepts it; Jetty preserves it verbatim so Spring rejects it. Switching containers
  surfaces the latent rejection with no client change.
• Regex identical in 6.5.11 and 7.1.0.

Suggested fix

Match 1*SP:

Pattern.compile("^Bearer +(?<token>[a-zA-Z0-9-._~+/]+=*)$", Pattern.CASE_INSENSITIVE);

Failing test

@Test
public void resolveWhenHeaderHasMultipleSpacesBeforeTokenThenTokenIsResolved() {
	// RFC 6750 section 2.1: credentials = "Bearer" 1*SP b64token (one or more spaces)
	MockHttpServletRequest request = new MockHttpServletRequest();
	request.addHeader("Authorization", "Bearer  " + TEST_TOKEN);
	assertThat(this.resolver.resolve(request)).isEqualTo(TEST_TOKEN);
}

Start with DefaultBearerTokenResolver and the resolver test containing resolveWhenHeaderHasMultipleSpacesBeforeTokenThenTokenIsResolved. Run that test to reproduce rejection of the double-space Authorization header, then verify that a valid token is resolved and reaches normal validation when one or more spaces follow Bearer.