GetTokenConfigFromEnv function gets a list of token service keys from environment variable and populates the default configuration with default token parameters and policies the function returns a TokenConfFile map instance and error if any if the environment variable is not present or the value of that is empty then it will return empty map if the value for the list is not well-formed, not comma-separated then it will return an error.

NewTokenProvider creates a new TokenProvider.

TokenProvider is the interface that the main program expects for implemeneting token generation.