fix: decode URL-encoded client ID and secret in Basic auth (#1263)

backend/internal/controller/oidc_controller.go

@@ -164,7 +164,7 @@ func (oc *OidcController) createTokensHandler(c *gin.Context) {
 
 	// Client id and secret can also be passed over the Authorization header
 	if input.ClientID == "" && input.ClientSecret == "" {
-		input.ClientID, input.ClientSecret, _ = c.Request.BasicAuth()
+		input.ClientID, input.ClientSecret, _ = utils.OAuthClientBasicAuth(c.Request)
 	}
 
 	tokens, err := oc.oidcService.CreateTokens(c.Request.Context(), input)
@@ -322,7 +322,7 @@ func (oc *OidcController) introspectTokenHandler(c *gin.Context) {
 		creds service.ClientAuthCredentials
 		ok    bool
 	)
-	creds.ClientID, creds.ClientSecret, ok = c.Request.BasicAuth()
+	creds.ClientID, creds.ClientSecret, ok = utils.OAuthClientBasicAuth(c.Request)
 	if !ok {
 		// If there's no basic auth, check if we have a bearer token
 		bearer, ok := utils.BearerAuth(c.Request)
@@ -659,7 +659,7 @@ func (oc *OidcController) deviceAuthorizationHandler(c *gin.Context) {
 
 	// Client id and secret can also be passed over the Authorization header
 	if input.ClientID == "" && input.ClientSecret == "" {
-		input.ClientID, input.ClientSecret, _ = c.Request.BasicAuth()
+		input.ClientID, input.ClientSecret, _ = utils.OAuthClientBasicAuth(c.Request)
 	}
 
 	response, err := oc.oidcService.CreateDeviceAuthorization(c.Request.Context(), input)

backend/internal/utils/http_util.go

@@ -2,6 +2,7 @@ package utils
 
 import (
 	"net/http"
+	"net/url"
 	"strconv"
 	"strings"
 	"time"
@@ -21,6 +22,27 @@ func BearerAuth(r *http.Request) (string, bool) {
 	return "", false
 }
 
+// OAuthClientBasicAuth returns the OAuth client ID and secret provided in the request's
+// Authorization header, if present. See RFC 6749, Section 2.3.
+func OAuthClientBasicAuth(r *http.Request) (clientID, clientSecret string, ok bool) {
+	clientID, clientSecret, ok = r.BasicAuth()
+	if !ok {
+		return "", "", false
+	}
+
+	clientID, err := url.QueryUnescape(clientID)
+	if err != nil {
+		return "", "", false
+	}
+
+	clientSecret, err = url.QueryUnescape(clientSecret)
+	if err != nil {
+		return "", "", false
+	}
+
+	return clientID, clientSecret, true
+}
+
 // SetCacheControlHeader sets the Cache-Control header for the response.
 func SetCacheControlHeader(ctx *gin.Context, maxAge, staleWhileRevalidate time.Duration) {
 	_, ok := ctx.GetQuery("skipCache")

backend/internal/utils/http_util_test.go

@@ -63,3 +63,62 @@ func TestBearerAuth(t *testing.T) {
 		})
 	}
 }
+
+func TestOAuthClientBasicAuth(t *testing.T) {
+	tests := []struct {
+		name                 string
+		authHeader           string
+		expectedClientID     string
+		expectedClientSecret string
+		expectedOk           bool
+	}{
+		{
+			name:                 "Valid client ID and secret in header (example from RFC 6749)",
+			authHeader:           "Basic czZCaGRSa3F0Mzo3RmpmcDBaQnIxS3REUmJuZlZkbUl3",
+			expectedClientID:     "s6BhdRkqt3",
+			expectedClientSecret: "7Fjfp0ZBr1KtDRbnfVdmIw",
+			expectedOk:           true,
+		},
+		{
+			name:             "Valid client ID and secret in header (escaped values)",
+			authHeader:       "Basic ZTUwOTcyYmQtNmUzMi00OTU3LWJhZmMtMzU0MTU3ZjI1NDViOislMjUlMjYlMkIlQzIlQTMlRTIlODIlQUM=",
+			expectedClientID: "e50972bd-6e32-4957-bafc-354157f2545b",
+			// This is the example string from RFC 6749, Appendix B.
+			expectedClientSecret: " %&+£€",
+			expectedOk:           true,
+		},
+		{
+			name:                 "Empty auth header",
+			authHeader:           "",
+			expectedClientID:     "",
+			expectedClientSecret: "",
+			expectedOk:           false,
+		},
+		{
+			name:                 "Basic prefix only",
+			authHeader:           "Basic ",
+			expectedClientID:     "",
+			expectedClientSecret: "",
+			expectedOk:           false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req, err := http.NewRequestWithContext(t.Context(), http.MethodGet, "http://example.com", nil)
+			require.NoError(t, err, "Failed to create request")
+
+			if tt.authHeader != "" {
+				req.Header.Set("Authorization", tt.authHeader)
+			}
+
+			clientId, clientSecret, ok := OAuthClientBasicAuth(req)
+
+			assert.Equal(t, tt.expectedOk, ok)
+
+			if tt.expectedOk {
+				assert.Equal(t, tt.expectedClientID, clientId)
+				assert.Equal(t, tt.expectedClientSecret, clientSecret)
+			}
+		})
+	}
+}