[auth/gcp] Adding basic google web auth flow capabilities (nytimes#231)

* initial WIP

* removing IAM verifier, cleaning up verify logic

* docs

* hooking in custom exception func

* renaming file

* removing unneeded client

* ensuring cookie is cleared

* cleaning up var declarations

* fixing the logger

* Forbids instead of redirecting

* cleaned up verify logic

* state cleanup

* simplifying logic

* avoiding a verify of an empty token

* adding some initial authenticator tests, callback still needs coverage

* adding some callback tests

* making notes in README

add http listen addr to config (nytimes#230)

* go fmt

* add HTTPAddr to config to allow configuring listen address

[server/kit] Adding log "format" functions that mimic `appengine/log` (…

…nytimes#229)

* tidying up example deps

* adding log*f funcs for the kit server

* variable firx

* adding more test logging

* DRY-ing things up a tad

tidying up example dependencies + updating go-kit (nytimes#227)

* tidying up example deps

* updating go-kit

* also updating example go-kit

Clean-up indirect dependencies (nytimes#226)

sarama was causing some other indirect dependencies. Upgrading it fixes
the issue.

We now have 3 indirect dependencies listed in go.mod:

- github.com/go-logfmt/logfmt
- github.com/go-stack/stack
- gopkg.in/jcmturner/goidentity.v3

go-kit accounts for the first two and sarama for the last one. Since
sarama does support go modules, this may be something missing on their
side.

go.mod: update ocagent to fix incorrect pseudo version (nytimes#225)

* go.mod: update ocagent to fix incorrect pseudo version

* update stackdriver

[server] Avoiding Prometheus memory bomb when using the new stdlib ro…

…uter (nytimes#223)

* no longer using prom instrumentation if using the stdlib router

* docs and downhill updates

[server] fixing stdlib router 😅 (nytimes#222)

* adding tests to fix stdlib router in server bc we shouldve done it from the start

* better test error msgs

adding a stdlib router to use in the server package (nytimes#221)

Adding log levels to kit/server.Log*Msg funcs (nytimes#220)

* adding log levels to kit/server.Log*Msg funcs. resolves nytimes#13

* adding warn and debug loggers, updating docs

* adding tests