Init sets the package-level config, which will used for token issuing and parsing in this package.

Parse uses the specified key to parse the token.

ParseRequest is used to parse the token from the Authorization header and passes it to the Parse function for Token parsing.

Sign issues a token using jwtSecret the token's claims will contain the provided subject.

ErrMissingHeader represent the error when the `Authorization` header is empty.

Config is the configuration for the token package.