encode
- string encode(string[string] payload, string key, JwtAlgorithm algo, string[string] header_fields)
- string encode(JSONValue payload, string key, JwtAlgorithm algo, JSONValue header_fields)
- string encode(ubyte[] payload, string key, JwtAlgorithm algo, JSONValue header_fields)
- string encode(string payload, string key, JwtAlgorithm algo, string header_fields)
simple version that accepts only strings as values for payload and header fields