feat: token introspection (#83)

* introspect

* introspect and client assertion

* introspect and client assertion

* scopes

* token introspection

* introspect

* refactoring

* fixes

* clenaup

* Update example/internal/mock/storage.go

Co-authored-by: Fabi <38692350+fgerschwiler@users.noreply.github.com>

* clenaup

Co-authored-by: Fabi <38692350+fgerschwiler@users.noreply.github.com>

pkg/client/rp/cli/cli.go

@@ -0,0 +1,35 @@
+package cli
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/caos/oidc/pkg/client/rp"
+	"github.com/caos/oidc/pkg/oidc"
+	"github.com/caos/oidc/pkg/utils"
+)
+
+const (
+	loginPath = "/login"
+)
+
+func CodeFlow(relyingParty rp.RelyingParty, callbackPath, port string, stateProvider func() string) *oidc.Tokens {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var token *oidc.Tokens
+	callback := func(w http.ResponseWriter, r *http.Request, tokens *oidc.Tokens, state string) {
+		token = tokens
+		msg := "<p><strong>Success!</strong></p>"
+		msg = msg + "<p>You are authenticated and can now return to the CLI.</p>"
+		w.Write([]byte(msg))
+	}
+	http.Handle(loginPath, rp.AuthURLHandler(stateProvider, relyingParty))
+	http.Handle(callbackPath, rp.CodeExchangeHandler(callback, relyingParty))
+
+	utils.StartServer(ctx, port)
+
+	utils.OpenBrowser("http://localhost:" + port + loginPath)
+
+	return token
+}