fernet acceptance tests


generate.json

	contains all parameters needed to deterministically generate
	a fernet token, as well as the token that should be generated.

	src: payload to be encrypted
	iv: 16-byte IV to use for encryption
	secret: base64-encoded 32-byte key to use for signing and encryption
	now: time to be used for the timestamp in the generated token
	token: value of the token that should be generated


verify.json

	contains a valid token and all parameters needed to deterministically
	verify it.

	token: token to be verified
	ttl_sec: time-to-live in seconds
	now: current time of the verifying process
	secret: base64-encoded 32-byte key to use for signing and decryption
	src: unencrypted payload to be retrieved from the token


invalid.json

	contains parameters for verification and a token that is invalid
	under those parameters, as well as a description of why the token
	is invalid.

	desc: reason why the token is invalid
	token: invalid token
	ttl_sec: time-to-live in seconds
	now: current time of the verifying process
	secret: base64-encoded 32-byte key to use for signing and decryption