Function extract_request_basic_credentials 

pub fn extract_request_basic_credentials<B>(
    request: &Request<B>,
) -> Result<Option<&str>, Error>

Extract raw Basic credentials from a complete request.

This reads request.headers() and delegates to extract_header_basic_credentials, preserving its missing, scheme-mismatch, empty-credential, and field-error behavior. No validation, decoding, or authentication is performed.