Add SHA384

[l1h3r]

Description of change

Adds SHA384 for JSON web tokens used in identity.rs

Type of change

• Enhancement (a non-breaking change which adds functionality)

How the change has been tested

Copied existing test structure using RFC test vectors and ones generated with python

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[Wollac]

Can the test vectors be moved into a different file? sha.rs has gotten so big, that it cannot be reviewed in GitHub. Maybe under tests similar to curl and blake?
Also, ideally the test vectors should be in a separate file than the test code. That way, the code can be checked and diff'ed without having to look at megabytes of test data.

[Wollac]

lgtm