# Constants
ProtocolAPIKey will hold api key credential.
ProtocolBase64 will represents credential binary data in base64
Storage service like gcs will take token files as input, we provide base64 protocol so that user can pass token binary data directly.
ProtocolEnv will represent credential from env.
ProtocolFile will hold file credential.
ProtocolHmac will hold access key and secret key credential.
# Variables
ErrInvalidValue means value is invalid.
ErrUnsupportedProtocol means protocol is unsupported.