Function parseWWWAuthenticate

parseWWWAuthenticate(
header: string | null | undefined,
): WWWAuthenticateChallenge | null
Parse a WWW-Authenticate header into its auth-scheme and parameters.

Handles the single-challenge case used by MCP servers in practice: one scheme (typically Bearer) followed by comma-separated key=value or key="value" auth-params. Returns null for an empty or malformed header.

Quoted-string values may contain escaped quotes (\") and backslashes (\\), per RFC 9110 §5.6.4; these are unescaped on the way out.
Parameters
- header: string | null | undefined
Returns WWWAuthenticateChallenge | null
Example
```
const c = parseWWWAuthenticate(
  'Bearer realm="api", error="invalid_token", resource_metadata="https://api.example.com/.well-known/oauth-protected-resource"'
);
// c.scheme === 'bearer'
// c.error === 'invalid_token'
// c.resource_metadata === 'https://api.example.com/.well-known/oauth-protected-resource'
```
- Defined in src/lib/auth/oauth/diagnostics.ts:55