Add support for *CBC+HS* encryption

[connor4312]

This PR adds support A128CBC+HS256, A192CBC+HS384, and A256CBC+HS512 content encryption. This set of encryption algorithms is from an older version of the JOSE RFC but they can still be found in the wild (particularly when compatibility with older systems is required.)

[csstaub]

Hi, thanks for the pull request! I will be able to review this tomorrow. If you haven't already, make sure to sign Square's Individual Contributor License Agreement (applies to all contributors with commits). I can't accept contributions without the agreement. Thanks!

[connor4312]

Hi @csstaub, this contributed code from Microsoft, rather than an individual. Do you have a corporate CLA and/or an email address for legal contact?

[csstaub]

I will look into that, will get back to you.

[csstaub]

Hi @connor4312, you can contact me at [email protected] and we'll get this set up.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
0 out of 2 committers have signed the CLA.

:x: mwan-beam
:x: connor4312

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