all: refactor handler logic

- all: prefer `FormValues` to `ParseForm` with subsequent `Form.Get`s
- all: refactor authentication stack to be checked by middleware, and accessible via request context.
- all: replace http.ServeMux with gorilla/mux’s router
- all: replace custom CSRF checks with gorilla/csrf middleware
- authenticate: extract callback path as constant.
- internal/config: implement stringer interface for policy
- internal/cryptutil: add helper func `NewBase64Key`
- internal/cryptutil: rename `GenerateKey` to `NewKey`
- internal/cryptutil: rename `GenerateRandomString` to `NewRandomStringN`
- internal/middleware: removed alice in favor of gorilla/mux
- internal/sessions: remove unused `ValidateRedirectURI` and `ValidateClientSecret`
- internal/sessions: replace custom CSRF with gorilla/csrf fork that supports custom handler protection
- internal/urlutil: add `SignedRedirectURL` to create hmac'd URLs
- internal/urlutil: add `ValidateURL` helper to parse URL options
- internal/urlutil: add `GetAbsoluteURL` which takes a request and returns its absolute URL.
- proxy: remove holdover state verification checks; we no longer are setting sessions in any proxy routes so we don’t need them.
- proxy: replace un-named http.ServeMux with named domain routes.

Signed-off-by: Bobby DeSimone <bobbydesimone@gmail.com>

internal/sessions/state.go

@@ -10,9 +10,6 @@ import (
 	"github.com/pomerium/pomerium/internal/cryptutil"
 )
 
-// ErrExpired is an error for a expired sessions.
-var ErrExpired = fmt.Errorf("internal/sessions: expired session")
-
 // State is our object that keeps track of a user's session state
 type State struct {
 	AccessToken     string    `json:"access_token"`