For tools that don't like empty passwords, this change allows
one to set a shared secret password for all users.

Check email validity on all requests rather than only on login.

Google - continually use refresh token

* New SessionState to consolidate email, access token and refresh token
* split ServeHttp into individual methods
* log on session renewal
* log on access token refresh
* refactor cookie encription/decription and session state serialization

Google - use offline access token

Cookie Refresh Improvements

* refresh now calculated as duration from cookie set

Release Version Two

* bump version to 2.0
* remove --cookie-https-only option
* add windows build to dist.sh
* rename --cookie-key to --cookie-name

Native SSL support

Page defaults to Google sign in

Github provider "Invalid Account"

disable email validation

This adds a "*" option to --email-domain to disable email validation, and this renames `--google-apps-domain` to `--email-domain` for clarity across providers

Fix validator_test hang on Solaris, Plan 9

On these platforms, the `done <- true` statement in during TearDown() was
hanging, since the `watcher_unsupported.go` version was never draining the
channel. Also took the opportunity to update the WatchForUpdates() signature
to not return bool anymore.

Fix unsupported WatchForUpdates and build tags

Closes #105.

The `go1.1` constraint has been updated to `!go1.3` per
https://golang.org/pkg/go/build/#hdr-Build_Constraints and
https://github.com/go-fsnotify/fsnotify. Also, the existing call signature for
`WatchForUpdates()` in `watcher_unsupported.go` was stale.

rename example file which is referenced in the README

Naming Is Hard - project name change

Add Github Provider

Provide graceful shutdown of file watcher in tests

TestValidatorOverwriteEmailListViaRenameAndReplace was deadlocking on
Windows because, on Windows, fsnotify.Watcher will continue to watch a
renamed file using its new name. On other systems, it appears the watch on
a file is removed after a rename.

The fix is to explicitly remove the watch to ensure the watch is resumed
under the original name.

These test failures from #93 inspired this change:
https://travis-ci.org/bitly/google_auth_proxy/jobs/62474406
https://travis-ci.org/bitly/google_auth_proxy/jobs/62474407

Both tests exhibited this pattern:
2015/05/13 22:10:54 validating: is xyzzy@example.com valid? false
2015/05/13 22:10:54 watching interrupted on event: "/tmp/test_auth_emails_300880185": CHMOD
2015/05/13 22:10:54 watching resumed for /tmp/test_auth_emails_300880185
2015/05/13 22:10:54 reloading after event: "/tmp/test_auth_emails_300880185": CHMOD
panic: test timed out after 1m0s

[snip]

goroutine 175 [chan send]:
github.com/bitly/google_auth_proxy.(*ValidatorTest).TearDown(0xc2080bc330)
        /home/travis/gopath/src/github.com/bitly/google_auth_proxy/validator_test.go:27 +0x43
github.com/bitly/google_auth_proxy.TestValidatorOverwriteEmailListViaRenameAndReplace(0xc2080f2480)
        /home/travis/gopath/src/github.com/bitly/google_auth_proxy/validator_watcher_test.go:103 +0x3b9

[snip]

goroutine 177 [chan send]:
github.com/bitly/google_auth_proxy.func·017()
        /home/travis/gopath/src/github.com/bitly/google_auth_proxy/validator_test.go:34 +0x41

I realized that the spurious CHMOD events were causing calls to
`func() { updated <- true }` (from validator_test.go:34), which caused
the goroutine running the watcher to block. At the same time,
ValidatorTest.TearDown was blocked by trying to send into the `done` channel.
The solution was to create a flag that ensured only one value was ever sent
into the update channel.

This test failure from #92 inspired this change:
https://travis-ci.org/bitly/google_auth_proxy/jobs/62425336

2015/05/13 16:27:33 using authenticated emails file /tmp/test_auth_emails_952353477
2015/05/13 16:27:33 watching /tmp/test_auth_emails_952353477 for updates
2015/05/13 16:27:33 validating: is xyzzy@example.com valid? true
2015/05/13 16:27:33 watching interrupted on event: "/tmp/test_auth_emails_952353477": CHMOD
2015/05/13 16:27:33 watching resumed for /tmp/test_auth_emails_952353477
2015/05/13 16:27:33 reloading after event: "/tmp/test_auth_emails_952353477": CHMOD
2015/05/13 16:27:33 watching interrupted on event: "/tmp/test_auth_emails_952353477": REMOVE
2015/05/13 16:27:33 validating: is xyzzy@example.com valid? false
2015/05/13 16:27:33 watching resumed for /tmp/test_auth_emails_952353477
2015/05/13 16:27:33 reloading after event: "/tmp/test_auth_emails_952353477": REMOVE
2015/05/13 16:27:33 failed opening authenticated-emails-file="/tmp/test_auth_emails_952353477", open /tmp/test_auth_emails_952353477: no such file or directory

I believe that what happened was that the call to reload the file after the
second "reloading after event" lost the race when the test shut down and the
file was removed. This change introduces a `done` channel that ensures
outstanding actions complete and the watcher exits before the test removes the
file.