Skip two-factor selection if there's only one option.

feature/registration/src/main/java/org/signal/registration/screens/signallogincredentials/SignalLoginCredentialEntryViewModel.kt

@@ -30,6 +30,7 @@ import org.signal.registration.screens.aepentry.AepInput
 import org.signal.registration.screens.shared.AccountIdError
 import org.signal.registration.screens.shared.AccountIdFormat
 import org.signal.registration.screens.twofactorselection.TwoFactorMethod
+import org.signal.registration.screens.twofactorselection.toAuthenticationRoute
 import org.signal.registration.screens.util.navigateBack
 import org.signal.registration.screens.util.navigateTo
 
@@ -244,10 +245,13 @@ class SignalLoginCredentialEntryViewModel(
           }
           RegisterAccountError.TotpMissingOrIncorrect -> {
             // For now this error only means TOTP, but in the future it will indicate that some two-factor method is
-            // required, so we treat it generically and route through the method selection screen.
-            Log.w(TAG, "[Next] A two-factor code is required. Sending the user to two-factor method selection.")
+            // required, so we treat it generically and let the method list decide where to go.
+            val methods = listOf(TwoFactorMethod.AuthenticatorApp)
+            val route = methods.toAuthenticationRoute()
+
+            Log.w(TAG, "[Next] A two-factor code is required. Sending the user to $route.")
             stateEmitter(inputState.copy(isLoggingIn = false))
-            parentEventEmitter.navigateTo(RegistrationRoute.TwoFactorSelection(methods = listOf(TwoFactorMethod.AuthenticatorApp)))
+            parentEventEmitter.navigateTo(route)
           }
           is RegisterAccountError.InvalidRequest,
           is RegisterAccountError.InvalidReceiptCredentialPresentation,

feature/registration/src/main/java/org/signal/registration/screens/twofactorselection/TwoFactorMethod.kt

@@ -5,6 +5,8 @@
 
 package org.signal.registration.screens.twofactorselection
 
+import org.signal.registration.RegistrationRoute
+
 /**
  * Two-factor authentication methods that may be presented on the two-factor selection screen. Which ones are actually
  * offered depends on what the account has registered.
@@ -16,3 +18,15 @@ enum class TwoFactorMethod {
   /** A one-time code generated by the user's authenticator app. */
   AuthenticatorApp
 }
+
+/**
+ * The route to send the user to in order to authenticate with one of these [TwoFactorMethod]s. When they're all of the
+ * same kind, the selection screen has nothing to choose between, so we skip straight to that method. Multiple entries
+ * of a kind are fine: the service checks the credential against every one the account has registered.
+ */
+fun List<TwoFactorMethod>.toAuthenticationRoute(): RegistrationRoute {
+  return when (toSet().singleOrNull()) {
+    TwoFactorMethod.AuthenticatorApp -> RegistrationRoute.TotpEntry
+    else -> RegistrationRoute.TwoFactorSelection(methods = this)
+  }
+}

feature/registration/src/test/java/org/signal/registration/RegistrationEndToEndTest.kt

@@ -1938,14 +1938,16 @@ class RegistrationEndToEndTest {
     useExistingSignalLogin()
     enterSignalLogin(login)
 
-    // The service wants a second factor, so the user picks one and enters a code from it
-    waitForTag(TestTags.TWO_FACTOR_SELECTION_AUTHENTICATOR_APP_OPTION)
-    composeTestRule.onNodeWithTag(TestTags.TWO_FACTOR_SELECTION_AUTHENTICATOR_APP_OPTION).performClick()
+    // The authenticator app is the only second factor available, so the user lands straight on code entry
     waitForTag(CodeEntryFieldTestTags.digit(0))
     composeTestRule.onNodeWithTag(CodeEntryFieldTestTags.digit(0)).performTextInput(totp)
 
     waitFor("registration to complete") { registrationComplete }
 
+    assert(composeTestRule.onAllNodesWithTag(TestTags.TWO_FACTOR_SELECTION_AUTHENTICATOR_APP_OPTION).fetchSemanticsNodes().isEmpty()) {
+      "There was only one two-factor method, so the selection screen should have been skipped"
+    }
+
     assert(networkController.lastRegisterAccountRequest?.totp == totp.toInt()) { "Expected the entered code to be sent with the login but was ${networkController.lastRegisterAccountRequest}" }
     assert(storageController.committedData?.accountData?.e164 == null) { "Expected an account with no phone number" }
   }

feature/registration/src/test/java/org/signal/registration/screens/signallogincredentials/SignalLoginCredentialEntryViewModelTest.kt

@@ -50,7 +50,6 @@ import org.signal.registration.screens.aepentry.AepInput
 import org.signal.registration.screens.restoreselection.ArchiveRestoreOption
 import org.signal.registration.screens.restoreselection.RegisteredState
 import org.signal.registration.screens.shared.AccountIdError
-import org.signal.registration.screens.twofactorselection.TwoFactorMethod
 import java.io.IOException
 import java.util.UUID
 import kotlin.time.Duration
@@ -462,7 +461,7 @@ class SignalLoginCredentialEntryViewModelTest {
   }
 
   @Test
-  fun `NextClicked requiring a two-factor code navigates to two-factor selection offering only the authenticator app`() = runTest(testDispatcher) {
+  fun `NextClicked requiring a two-factor code navigates directly to TOTP entry`() = runTest(testDispatcher) {
     coEvery { mockRepository.reRegisterAccountWithoutPhoneNumber(any(), any(), any(), any(), any()) } returns
       RequestResult.NonSuccess(RegisterAccountError.TotpMissingOrIncorrect)
 
@@ -472,9 +471,7 @@ class SignalLoginCredentialEntryViewModelTest {
     assertThat(emittedParentEvents.last())
       .isInstanceOf<RegistrationFlowEvent.NavigateToScreen>()
       .prop(RegistrationFlowEvent.NavigateToScreen::route)
-      .isInstanceOf<RegistrationRoute.TwoFactorSelection>()
-      .prop(RegistrationRoute.TwoFactorSelection::methods)
-      .containsExactly(TwoFactorMethod.AuthenticatorApp)
+      .isEqualTo(RegistrationRoute.TotpEntry)
   }
 
   @Test