Release v13.21.0

See merge request gitlab-org/gitlab-shell!512

build: bump go version to 1.16

See merge request gitlab-org/gitlab-shell!509

ci: start integrating go 1.17 into the CI pipelines

See merge request gitlab-org/gitlab-shell!510

fix: validate client cert paths exist on disk before proceeding

Closes #486

See merge request gitlab-org/gitlab-shell!508

refactor: update usage of NewHTTPClient to NewHTTPClientWithOpts

Closes #484

See merge request gitlab-org/gitlab-shell!507

build: bump go to 1.15

See merge request gitlab-org/gitlab-shell!505

Switch to labkit for logging system setup

Closes #271

See merge request gitlab-org/gitlab-shell!504

- We start supporting the "color" format for logs.
- We now respond to SIGHUP by reopening the log file.
- We now respect the log format when no log filename is specified.

Output to syslog in the event of logging system setup is preserved in
OpenSSH mode.

Changelog: added

Modify regex to prevent partial matches

See merge request gitlab-org/security/gitlab-shell!6

Remove some unreliable tests

Closes #477

See merge request gitlab-org/gitlab-shell!503

Logrus buffers its output internally, which makes these tests fail
intermittently. They're also not a good example to follow generally.

We now have acceptance tests that exercise this functionality so I'm
pretty relaxed about losing the expectations. However, we can test
them by inspecting the server-received metadata too, so there's no loss
of coverage here.

The move from logrus to labkit for logging also makes these tests hard
to justify keeping.

Log same correlation_id on auth keys check of ssh connections

See merge request gitlab-org/gitlab-shell!501

Update go-proxyproto to v0.6.0

See merge request gitlab-org/gitlab-shell!499

Make gofmt check fail if there are any matching files

See merge request gitlab-org/gitlab-shell!500

gofmt doesn't return an exit code 1 if there are matching files:
https://github.com/golang/go/issues/24230

To fix this, use the same trick we use in Workhorse to parse output.
Also add a `make fmt` step to format all the code properly.

From https://github.com/pires/go-proxyproto/releases:

Prevent potentially malicious client(s) from opening connections and not
send the proxy protocol header, which could lead to DoS as the server
would hold those socket descriptors open indefinitely, eventually
running out of resources. The solution is to set a read deadline when
waiting for the PROXY protocol header:
https://github.com/pires/go-proxyproto/pull/74

Switch to labkit/log for logging functionality

See merge request gitlab-org/gitlab-shell!498

Unit tests for internal/sshd/connection.go

Closes #521

See merge request gitlab-org/gitlab-shell!497

Prometheus metrics for HTTP requests

See merge request gitlab-org/gitlab-shell!496

A RoundTripper for tracking the duration of an http request
is introduced

Add tracing instrumentation to http client

See merge request gitlab-org/gitlab-shell!495