BuildJWTString generates a JWT (JSON Web Token) string containing a unique user ID and an expiration time.

GenerateRandomUserID generates a random alphanumeric user ID of the specified length.

GetTLSCertificate generates a self-signed TLS certificate and returns its PEM-encoded certificate and private key.

GetUserIDByToken extracts and validates the user ID from a JWT string.

SaveToFile writes the given content to a file with the specified filename.

Claims represents the custom claims embedded in the JWT (JSON Web Token).