Add a new provider for Bitbucket,
can be configured from the options
specifying team and/or repository
that the user must be part/have access
to in order to grant login.

Made setting of proxied headers deterministic based on configuration alone

alone

Previously some headers that are normally set by the proxy (and may be
replied upstream for authorization decisiions) were not being set
depending on values in the users sesssion.

This change ensure that if a given header is sometimes set, it will
always be either set or removed.

It might be worth considerating always deleting these headers if we
didn't add them.

Fix links in docs

Docs only:  format Command Line Options using a table

Fix some typos

Add OIDC support for UserInfo Endpoint Email Verification

- Fixed a bunch of references to the repo, which were 404ing
- Fixed a couple of things that 301/302ed
- Fixed some in page references

[docs] Fix link to oauth2_proxy.cfg

Fix typos in changelog

* New flag "-ssl-upstream-insecure-skip-validation" to skip SSL validation for upstreams with self generated / invalid SSL certificates.

* Fix tests for modified NewReverseProxy method.

* Added change to the changelog.

* Remove duplicate entries from changelog.

* Adding documentation for Okta OIDC provider.

* additional clean up.

* Clearer heading

* Forgot a word.

* updated documentation based on ReillyProcentive review.

* Per steakunderscore review: removed defaults. Removed extra hardening steps (expiration, https only etc) not directly related to setting up Okta w/ OIDC

Adds reference to slack channel in readme

* Initial version of OIDC based GitLab provider

* Add support for email domain check to GitLab provider

* Add gitlab.com as default issuer for GitLab provider

* Update documentation for GitLab provider

* Update unit tests for new GitLab provider implementation

* Update CHANGELOG for GitLab provider

* Rename GitLab test access token as response to linter

* Check Google group membership with hasMember and get.

This PR is an enhancement built on
https://github.com/pusher/oauth2_proxy/pull/160. That PR reduces the
number of calls to the Google Admin API and simplifies the code by
using the hasMember method. It also supports checking membership in
nested groups.

However, the above message doesn't handle members who are not a part
of the domain. The hasMember API returns a 400 for that case. As a
fallback, when the API returns a 400, this change will try using the
`get` API which works as expected for members who aren't a part of the
domain. Supporting members who belong to the Google group but aren't
part of the domain is a requested feature from
https://github.com/pusher/oauth2_proxy/issues/95.

https://developers.google.com/admin-sdk/directory/v1/reference/members/get

Note that nested members who are not a part of the domain will not be
correctly detected with this change.

* Update CHANGELOG.

* Fix incorrect JSON and stop escaping strings.

* Add comments for each scenario.

[DOCS] Fix a bunch of places where the repo link was incorrect

Remove dep from Travis CI & pre-install modules

Was missed from previous switch to go modules

Fix CODEOWNERS file