fn parse_basic_credentials(header: &str) -> Option<(String, String)>Expand description
Parses an Authorization: Basic ... header value into (username, password).
Mirrors the APISIX Lua: the scheme match is case-insensitive, the payload is
standard-base64 decoded, split on the first :, and all whitespace is
stripped from both fields. Returns None when the header is not Basic,
the payload is not valid base64/UTF-8, or there is no : separator.