controlplane: add well-known endpoint to the controlplane http handler (#3555)

* controlplane: add well-known endpoint to the controlplane http handler

* add support for trailing /

* remove redundant test

internal/controlplane/server_test.go

@@ -0,0 +1,55 @@
+package controlplane
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/pomerium/pomerium/config"
+	"github.com/pomerium/pomerium/internal/events"
+	"github.com/pomerium/pomerium/pkg/netutil"
+)
+
+func TestServerWellKnown(t *testing.T) {
+	ports, err := netutil.AllocatePorts(5)
+	require.NoError(t, err)
+
+	ctx := context.Background()
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	cfg := &config.Config{
+		GRPCPort:     ports[0],
+		HTTPPort:     ports[1],
+		OutboundPort: ports[2],
+		MetricsPort:  ports[3],
+		DebugPort:    ports[4],
+
+		Options: config.NewDefaultOptions(),
+	}
+	cfg.Options.AuthenticateURLString = "https://authenticate.localhost.pomerium.io"
+	src := config.NewStaticSource(cfg)
+	srv, err := NewServer(cfg, config.NewMetricsManager(ctx, src), events.New())
+	require.NoError(t, err)
+	go srv.Run(ctx)
+
+	res, err := http.Get(fmt.Sprintf("http://localhost:%s/.well-known/pomerium", src.GetConfig().HTTPPort))
+	require.NoError(t, err)
+	defer res.Body.Close()
+
+	var actual map[string]any
+	err = json.NewDecoder(res.Body).Decode(&actual)
+	require.NoError(t, err)
+
+	expect := map[string]any{
+		"authentication_callback_endpoint": "https://authenticate.localhost.pomerium.io/oauth2/callback",
+		"frontchannel_logout_uri":          "https://authenticate.localhost.pomerium.io/.pomerium/sign_out",
+		"jwks_uri":                         "https://authenticate.localhost.pomerium.io/.well-known/pomerium/jwks.json",
+	}
+	assert.Equal(t, expect, actual)
+}