Go kit: stringsvc2 with JWT

Go kit
stringsvc2

As part of learning Go Kit, now I'm trying to add JWT to stringsvc2.

• Use custom claims to save client ID in JWT
• Add /auth endpoint for getting a token
• Protect /uppercase and /count endpoints with JWT
• Use Context to pass client ID
• Log client ID and record client ID in metrics
• Protect /metrics endpoint with basic auth

go build -o server
./server

curl -v -XPOST -d '{"clientId": "mobile", "clientSecret": "m_secret"}' http://localhost:8080/auth

curl -v -XPOST -d '{"s": "hello world"}' -H "Authorization: Bearer eyJhbGci..." http://localhost:8080/uppercase

curl -v --user prometheus:password http://localhost:8080/metrics