feat: get issuer from context for device auth (#363)

* feat: get issuer from context for device auth

* use distinct UserFormURL and UserFormPath

- Properly deprecate UserFormURL and default to old behaviour,
to prevent breaking change.

- Refactor unit tests to test both cases.

* update example

example/server/exampleop/op.go

@@ -107,7 +107,7 @@ func newOP(storage op.Storage, issuer string, key [32]byte) (op.OpenIDProvider,
 		DeviceAuthorization: op.DeviceAuthorizationConfig{
 			Lifetime:     5 * time.Minute,
 			PollInterval: 5 * time.Second,
-			UserFormURL:  issuer + "device",
+			UserFormPath: "/device",
 			UserCode:     op.UserCodeBase20,
 		},
 	}

pkg/op/device.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"math/big"
 	"net/http"
+	"net/url"
 	"strings"
 	"time"
 
@@ -18,7 +19,14 @@ import (
 type DeviceAuthorizationConfig struct {
 	Lifetime     time.Duration
 	PollInterval time.Duration
-	UserFormURL  string // the URL where the user must go to authorize the device
+
+	// UserFormURL is the complete URL where the user must go to authorize the device.
+	// Deprecated: use UserFormPath instead.
+	UserFormURL string
+
+	// UserFormPath is the path where the user must go to authorize the device.
+	// The hostname for the URL is taken from the request by IssuerFromContext.
+	UserFormPath string
 	UserCode     UserCodeConfig
 }
 
@@ -82,15 +90,28 @@ func DeviceAuthorization(w http.ResponseWriter, r *http.Request, o OpenIDProvide
 		return err
 	}
 
+	var verification *url.URL
+	if config.UserFormURL != "" {
+		if verification, err = url.Parse(config.UserFormURL); err != nil {
+			return oidc.ErrServerError().WithParent(err).WithDescription("invalid URL for device user form")
+		}
+	} else {
+		if verification, err = url.Parse(IssuerFromContext(r.Context())); err != nil {
+			return oidc.ErrServerError().WithParent(err).WithDescription("invalid URL for issuer")
+		}
+		verification.Path = config.UserFormPath
+	}
+
 	response := &oidc.DeviceAuthorizationResponse{
 		DeviceCode:      deviceCode,
 		UserCode:        userCode,
-		VerificationURI: config.UserFormURL,
+		VerificationURI: verification.String(),
 		ExpiresIn:       int(config.Lifetime / time.Second),
 		Interval:        int(config.PollInterval / time.Second),
 	}
 
-	response.VerificationURIComplete = fmt.Sprintf("%s?user_code=%s", config.UserFormURL, userCode)
+	verification.RawQuery = "user_code=" + userCode
+	response.VerificationURIComplete = verification.String()
 
 	httphelper.MarshalJSON(w, response)
 	return nil

pkg/op/device_test.go

@@ -13,6 +13,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/muhlemmer/gu"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"github.com/zitadel/oidc/v2/pkg/oidc"
@@ -20,29 +21,60 @@ import (
 )
 
 func Test_deviceAuthorizationHandler(t *testing.T) {
-	req := &oidc.DeviceAuthorizationRequest{
-		Scopes:   []string{"foo", "bar"},
-		ClientID: "web",
+	type conf struct {
+		UserFormURL  string
+		UserFormPath string
 	}
-	values := make(url.Values)
-	testProvider.Encoder().Encode(req, values)
-	body := strings.NewReader(values.Encode())
+	tests := []struct {
+		name string
+		conf conf
+	}{
+		{
+			name: "UserFormURL",
+			conf: conf{
+				UserFormURL: "https://localhost:9998/device",
+			},
+		},
+		{
+			name: "UserFormPath",
+			conf: conf{
+				UserFormPath: "/device",
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			conf := gu.PtrCopy(testConfig)
+			conf.DeviceAuthorization.UserFormURL = tt.conf.UserFormURL
+			conf.DeviceAuthorization.UserFormPath = tt.conf.UserFormPath
+			provider := newTestProvider(conf)
 
-	r := httptest.NewRequest(http.MethodPost, "/", body)
-	r.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+			req := &oidc.DeviceAuthorizationRequest{
+				Scopes:   []string{"foo", "bar"},
+				ClientID: "web",
+			}
+			values := make(url.Values)
+			testProvider.Encoder().Encode(req, values)
+			body := strings.NewReader(values.Encode())
 
-	w := httptest.NewRecorder()
+			r := httptest.NewRequest(http.MethodPost, "/", body)
+			r.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+			r = r.WithContext(op.ContextWithIssuer(r.Context(), testIssuer))
 
-	runWithRandReader(mr.New(mr.NewSource(1)), func() {
-		op.DeviceAuthorizationHandler(testProvider)(w, r)
-	})
+			w := httptest.NewRecorder()
 
-	result := w.Result()
+			runWithRandReader(mr.New(mr.NewSource(1)), func() {
+				op.DeviceAuthorizationHandler(provider)(w, r)
+			})
 
-	assert.Less(t, result.StatusCode, 300)
+			result := w.Result()
 
-	got, _ := io.ReadAll(result.Body)
-	assert.JSONEq(t, `{"device_code":"Uv38ByGCZU8WP18PmmIdcg", "expires_in":300, "interval":5, "user_code":"JKRV-FRGK", "verification_uri":"https://localhost:9998/device", "verification_uri_complete":"https://localhost:9998/device?user_code=JKRV-FRGK"}`, string(got))
+			assert.Less(t, result.StatusCode, 300)
+
+			got, _ := io.ReadAll(result.Body)
+			assert.JSONEq(t, `{"device_code":"Uv38ByGCZU8WP18PmmIdcg", "expires_in":300, "interval":5, "user_code":"JKRV-FRGK", "verification_uri":"https://localhost:9998/device", "verification_uri_complete":"https://localhost:9998/device?user_code=JKRV-FRGK"}`, string(got))
+		})
+	}
 }
 
 func TestParseDeviceCodeRequest(t *testing.T) {

pkg/op/op_test.go

@@ -20,15 +20,9 @@ import (
 	"golang.org/x/text/language"
 )
 
-var testProvider op.OpenIDProvider
-
-const (
-	testIssuer    = "https://localhost:9998/"
-	pathLoggedOut = "/logged-out"
-)
-
-func init() {
-	config := &op.Config{
+var (
+	testProvider op.OpenIDProvider
+	testConfig   = &op.Config{
 		CryptoKey:                sha256.Sum256([]byte("test")),
 		DefaultLogoutRedirectURI: pathLoggedOut,
 		CodeMethodS256:           true,
@@ -40,24 +34,35 @@ func init() {
 		DeviceAuthorization: op.DeviceAuthorizationConfig{
 			Lifetime:     5 * time.Minute,
 			PollInterval: 5 * time.Second,
-			UserFormURL:  testIssuer + "device",
+			UserFormPath: "/device",
 			UserCode:     op.UserCodeBase20,
 		},
 	}
+)
 
+const (
+	testIssuer    = "https://localhost:9998/"
+	pathLoggedOut = "/logged-out"
+)
+
+func init() {
 	storage.RegisterClients(
 		storage.NativeClient("native"),
 		storage.WebClient("web", "secret", "https://example.com"),
 		storage.WebClient("api", "secret"),
 	)
 
-	var err error
-	testProvider, err = op.NewOpenIDProvider(testIssuer, config,
+	testProvider = newTestProvider(testConfig)
+}
+
+func newTestProvider(config *op.Config) op.OpenIDProvider {
+	provider, err := op.NewOpenIDProvider(testIssuer, config,
 		storage.NewStorage(storage.NewUserStore(testIssuer)), op.WithAllowInsecure(),
 	)
 	if err != nil {
 		panic(err)
 	}
+	return provider
 }
 
 type routesTestStorage interface {