Encryption of JWTs

[stravid87]

Description
Nice work on the JWTs. Now that all three are where they need to be, time to add some security so that they aren't sent in clear text.

Notes

• If we're lucky, the JWT library you have used already incorporates JWT encryption and we just need to supply a private key.
• You can use the same private key to in the rp to encrypt both the fp_rp_jwt, & int_rp_jwt.
• The JWT signing key should be different from the JWT encryption key.
• The addition of encryption adds confidentiality to the JWTs. This is in addition to the authentication already being supplied through signing.

Acceptance Criteria

• All three JWTs shown are encrypted: int_fp_jwt, fp_rp_jwt, & int_rp_jwt
• A JWT encryption key is included in the .env of the FP & RP

[dtpthao]

Well, we are not lucky because we currently use jsonwebtoken, which only supports JWS. I'll switch to this https://github.com/hidekatsu-izuno/josekit-rs

[stravid87]

Okay. I accept. This was a more challenging problem than I suspected and possibly unnecessary.