Opium.AuthSourceAuthentication functions to work with common HTTP authentication methods.
string_of_credentialstring_of_credential cred converts the credentials into a string usable in the Authorization header.
credential_of_stringcredential_of_string s parses a string from the Authorization header into credentials.
string_of_challengestring_of_challenge challenge converts the challenge into a string usable in the WWW-Authenticate response header.