def to_jwe(self, keys, enc, alg, lev=<NUM_LIT:0>):
_jwe = JWE(self.to_json(lev), alg=alg, enc=enc)<EOL>return _jwe.encrypt(keys)<EOL>
Place the information in this instance in a JSON object. Make that
JSON object the body of a JWT. Then encrypt that JWT using the
specified algorithms and the given keys. Return the encrypted JWT.

:param keys: list or KeyJar instance
:param enc: Content Encryption Algorithm
:param alg: Key Management Algorithm
:param lev: Used for JSON construction
:return: An encrypted JWT. If encryption failed an exception will be
    raised.