fix(server): first user created should be admin, when using reverse proxy

Fix #3902

Signed-off-by: Deluan <deluan@navidrome.org>

server/auth.go

@@ -292,13 +292,17 @@ func handleLoginFromHeaders(ds model.DataStore, r *http.Request) map[string]inte
 	user, err := userRepo.FindByUsernameWithPassword(username)
 	if user == nil || err != nil {
 		log.Info(r, "User passed in header not found", "user", username)
+		// Check if this is the first user being created
+		count, _ := userRepo.CountAll()
+		isFirstUser := count == 0
+
 		newUser := model.User{
 			ID:          id.NewRandom(),
 			UserName:    username,
 			Name:        username,
 			Email:       "",
 			NewPassword: consts.PasswordAutogenPrefix + id.NewRandom(),
-			IsAdmin:     false,
+			IsAdmin:     isFirstUser, // Make the first user an admin
 		}
 		err := userRepo.Put(&newUser)
 		if err != nil {

server/auth_test.go

@@ -292,4 +292,54 @@ var _ = Describe("Auth", func() {
 			})
 		})
 	})
+
+	Describe("handleLoginFromHeaders", func() {
+		var ds model.DataStore
+		var req *http.Request
+		const trustedIP = "192.168.0.42"
+
+		BeforeEach(func() {
+			ds = &tests.MockDataStore{}
+			req = httptest.NewRequest("GET", "/", nil)
+			req = req.WithContext(request.WithReverseProxyIp(req.Context(), trustedIP))
+			conf.Server.ReverseProxyWhitelist = "192.168.0.0/16"
+			conf.Server.ReverseProxyUserHeader = "Remote-User"
+		})
+
+		It("makes the first user an admin", func() {
+			// No existing users
+			req.Header.Set("Remote-User", "firstuser")
+			result := handleLoginFromHeaders(ds, req)
+
+			Expect(result).ToNot(BeNil())
+			Expect(result["isAdmin"]).To(BeTrue())
+
+			// Verify user was created as admin
+			u, err := ds.User(context.Background()).FindByUsername("firstuser")
+			Expect(err).To(BeNil())
+			Expect(u.IsAdmin).To(BeTrue())
+		})
+
+		It("does not make subsequent users admins", func() {
+			// Create the first user
+			_ = ds.User(context.Background()).Put(&model.User{
+				ID:       "existing-user-id",
+				UserName: "existinguser",
+				Name:     "Existing User",
+				IsAdmin:  true,
+			})
+
+			// Try to create a second user via proxy header
+			req.Header.Set("Remote-User", "seconduser")
+			result := handleLoginFromHeaders(ds, req)
+
+			Expect(result).ToNot(BeNil())
+			Expect(result["isAdmin"]).To(BeFalse())
+
+			// Verify user was created as non-admin
+			u, err := ds.User(context.Background()).FindByUsername("seconduser")
+			Expect(err).To(BeNil())
+			Expect(u.IsAdmin).To(BeFalse())
+		})
+	})
 })