chore: replace gorilla/mux with go-chi/chi (#332)

BREAKING CHANGE:
The returned router from `op.CreateRouter()` is now a `chi.Router`

Closes #301

example/server/exampleop/op.go

@@ -6,7 +6,7 @@ import (
 	"net/http"
 	"time"
 
-	"github.com/gorilla/mux"
+	"github.com/go-chi/chi"
 	"golang.org/x/text/language"
 
 	"github.com/zitadel/oidc/v2/example/server/storage"
@@ -34,12 +34,12 @@ type Storage interface {
 // SetupServer creates an OIDC server with Issuer=http://localhost:<port>
 //
 // Use one of the pre-made clients in storage/clients.go or register a new one.
-func SetupServer(issuer string, storage Storage) *mux.Router {
+func SetupServer(issuer string, storage Storage) chi.Router {
 	// the OpenID Provider requires a 32-byte key for (token) encryption
 	// be sure to create a proper crypto random key and manage it securely!
 	key := sha256.Sum256([]byte("test"))
 
-	router := mux.NewRouter()
+	router := chi.NewRouter()
 
 	// for simplicity, we provide a very small default page for users who have signed out
 	router.HandleFunc(pathLoggedOut, func(w http.ResponseWriter, req *http.Request) {
@@ -61,17 +61,18 @@ func SetupServer(issuer string, storage Storage) *mux.Router {
 
 	// regardless of how many pages / steps there are in the process, the UI must be registered in the router,
 	// so we will direct all calls to /login to the login UI
-	router.PathPrefix("/login/").Handler(http.StripPrefix("/login", l.router))
+	router.Mount("/login/", http.StripPrefix("/login", l.router))
 
-	router.PathPrefix("/device").Subrouter()
-	registerDeviceAuth(storage, router.PathPrefix("/device").Subrouter())
+	router.Route("/device", func(r chi.Router) {
+		registerDeviceAuth(storage, r)
+	})
 
 	// we register the http handler of the OP on the root, so that the discovery endpoint (/.well-known/openid-configuration)
 	// is served on the correct path
 	//
 	// if your issuer ends with a path (e.g. http://localhost:9998/custom/path/),
 	// then you would have to set the path prefix (/custom/path/)
-	router.PathPrefix("/").Handler(provider.HttpHandler())
+	router.Mount("/", provider)
 
 	return router
 }