# Functions
The function Base64Encode encodes a byte slice into a base64 string and removes any trailing equal signs.
The GenerateJWT function takes in a header, payload, and secret, encodes them into a JSON Web Token (JWT), signs the token using the secret, and returns the complete JWT.
The Sign function takes a data string and a secret key, and returns a base64-encoded HMAC-SHA256 signature of the data using the secret key.
# Structs
The above code defines a struct type called "Header" with two string fields, "Alg" and "Typ", which are tagged for JSON serialization.
# Interfaces
The above code defines an interface named Payload that has a method ToJSON() which returns a byte slice and an error.