Add route keys/{kid}/jwk.json

[Equanox]

JWK (https://tools.ietf.org/html/rfc7517) format seems to be a bit more common to expose the public key. This allows us to be more flexible in checking JWT validity.

I think it won't break anything as the pem route is still functional. The JWK creation is based on https://github.com/lestrrat-go/jwx .

[johnabass]

Nicely done. Let's push this in our next release.

We should add content negotiation to the /keys/{kid] endpoint to allow returning PEM or JWK, but that can be done in a follow-on PR.

[joe94]

I agree. This is great! 😄 Thanks, @Equanox! FYI: there are some failing tests in travis though. We should fix that before merging.

[Equanox]

Thx guys, will fix the failing tests. @johnabass didnt know exactly how to react properly to the Content-Type, is there a example in one of your repos? Then i will try to do a follow up PR.

[codecov-io]

Codecov Report

Merging #48 into master will decrease coverage by 1.12%.
The diff coverage is 73.33%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
- Coverage   96.60%   95.48%   -1.13%     
==========================================
  Files          38       39       +1     
  Lines        1209     1262      +53     
==========================================
+ Hits         1168     1205      +37     
- Misses         27       35       +8     
- Partials       14       22       +8     

Impacted Files	Coverage Δ
key/pair.go	77.53% <56.75%> (-8.45%)	⬇️
key/handler_jwk.go	100.00% <100.00%> (ø)
key/provide.go	100.00% <100.00%> (ø)

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[johnabass]

Thx guys, will fix the failing tests. @johnabass didnt know exactly how to react properly to the Content-Type, is there a example in one of your repos? Then i will try to do a follow up PR.

We're in the process of retooling around content negotiation. We should just push this PR to master for now. We can redo an URLs or content negotation after we settle on a solution.

[johnabass]

https://github.com/xmidt-org/themis/releases/tag/v0.4.4 has this PR in it.

I did change things a bit in #53. Notably, the specific URLs are /keys/{kid}/key.json and /keys/{kid}/keys.pem when not using content negotiation.