Adds app verification alternative (#228)

* Adds app verification alternative

11 files changed, 492 insertions, 51 deletions

diff --git a/AuthSamples/Sample/MainViewController.m b/AuthSamples/Sample/MainViewController.m
index bb8b07d..fb9bf67 100644
--- a/AuthSamples/Sample/MainViewController.m
+++ b/AuthSamples/Sample/MainViewController.m
@@ -37,6 +37,12 @@
 #import "UserInfoViewController.h"
 #import "UserTableViewCell.h"
 
+
+/*! @typedef textInputCompletionBlock
+    @brief The type of callback used to report text input prompt results.
+ */
+typedef void (^textInputCompletionBlock)(NSString *_Nullable userInput);
+
 /** @var kTokenGetButtonText
     @brief The text of the "Get Token" button.
  */
@@ -506,6 +512,11 @@ static NSString *const kPhoneAuthSectionTitle = @"Phone Auth";
  */
 static NSString *const kPhoneNumberSignInTitle = @"Sign in With Phone Number";
 
+/** @var kPhoneNumberSignInTitle
+    @brief The title for button to sign in with phone number using reCAPTCHA.
+ */
+static NSString *const kPhoneNumberSignInReCaptchaTitle = @"Sign in With Phone Number (reCAPTCHA)";
+
 /** @typedef showEmailPasswordDialogCompletion
     @brief The type of block which gets called to complete the Email/Password dialog flow.
  */
@@ -644,6 +655,8 @@ typedef enum {
                                            action:^{ [weakSelf presentSettings]; }]
       ]],
       [StaticContentTableViewSection sectionWithTitle:kPhoneAuthSectionTitle cells:@[
+        [StaticContentTableViewCell cellWithTitle:kPhoneNumberSignInReCaptchaTitle
+                                           action:^{ [weakSelf signInWithPhoneNumberRecaptcha]; }],
         [StaticContentTableViewCell cellWithTitle:kPhoneNumberSignInTitle
                                            action:^{ [weakSelf signInWithPhoneNumber]; }],
         [StaticContentTableViewCell cellWithTitle:kUpdatePhoneNumber
@@ -2399,14 +2412,9 @@ static NSDictionary<NSString *, NSString *> *parseURL(NSString *urlString) {
     @brief Allows sign in with phone number.
  */
 - (void)signInWithPhoneNumber {
-  [self showTextInputPromptWithMessage:@"Phone #:"
-                          keyboardType:UIKeyboardTypePhonePad
-                       completionBlock:^(BOOL userPressedOK, NSString *_Nullable phoneNumber) {
-    if (!userPressedOK || !phoneNumber.length) {
-      return;
-    }
+  [self commonPhoneNumberInputWithTitle:@"Phone #" Completion:^(NSString *_Nullable phone) {
     [self showSpinner:^{
-      [[AppManager phoneAuthProvider] verifyPhoneNumber:phoneNumber
+      [[AppManager phoneAuthProvider] verifyPhoneNumber:phone
                                              completion:^(NSString *_Nullable verificationID,
                                                           NSError *_Nullable error) {
         [self hideSpinner:^{
@@ -2417,29 +2425,10 @@ static NSDictionary<NSString *, NSString *> *parseURL(NSString *urlString) {
           }
           [self logSuccess:@"Code sent"];
 
-          [self showTextInputPromptWithMessage:@"Verification code:"
-                                  keyboardType:UIKeyboardTypeNumberPad
-                               completionBlock:^(BOOL userPressedOK,
-                                                 NSString *_Nullable verificationCode) {
-            if (!userPressedOK || !verificationCode.length) {
-              return;
-            }
-            [self showSpinner:^{
-              FIRAuthCredential *credential =
-                  [[AppManager phoneAuthProvider] credentialWithVerificationID:verificationID
-                                                              verificationCode:verificationCode];
-              [[AppManager auth] signInWithCredential:credential
-                                           completion:^(FIRUser *_Nullable user,
-                                                        NSError *_Nullable error) {
-                [self hideSpinner:^{
-                  if (error) {
-                    [self logFailure:@"failed to verify phone number" error:error];
-                    [self showMessagePrompt:error.localizedDescription];
-                    return;
-                  }
-                }];
-              }];
-            }];
+          [self commonPhoneNumberInputWithTitle:@"Code"
+                                     Completion:^(NSString *_Nullable verificationCode) {
+            [self commontPhoneVerificationWithVerificationID:verificationID
+                                            verificationCode:verificationCode];
           }];
         }];
       }];
@@ -2447,6 +2436,76 @@ static NSDictionary<NSString *, NSString *> *parseURL(NSString *urlString) {
   }];
 }
 
+/** @fn signInWithPhoneNumberRecaptcha
+    @brief Allows sign in with phone number using reCAPTCHA
+ */
+- (void)signInWithPhoneNumberRecaptcha {
+  [self commonPhoneNumberInputWithTitle:@"Phone #" Completion:^(NSString *_Nullable phone) {
+    [self showSpinner:^{
+      [[AppManager phoneAuthProvider] verifyPhoneNumber:phone
+                                             UIDelegate:nil
+                                             completion:^(NSString *_Nullable verificationID,
+                                                          NSError *_Nullable error) {
+        [self hideSpinner:^{
+          if (error) {
+            [self logFailure:@"failed to send verification code" error:error];
+            [self showMessagePrompt:error.localizedDescription];
+            return;
+          }
+          [self logSuccess:@"Code sent"];
+
+          [self commonPhoneNumberInputWithTitle:@"Code"
+                                     Completion:^(NSString *_Nullable verificationCode) {
+            [self commontPhoneVerificationWithVerificationID:verificationID
+                                            verificationCode:verificationCode];
+          }];
+        }];
+      }];
+    }];
+  }];
+}
+
+/** @fn commonPhoneNumberInputWithLabel:Completion
+    @brief Allows user input into a text field.
+    @param title of the promt.
+ */
+- (void)commonPhoneNumberInputWithTitle:(NSString *)title
+                             Completion:(textInputCompletionBlock)completion {
+  [self showTextInputPromptWithMessage:title
+                          keyboardType:UIKeyboardTypePhonePad
+                       completionBlock:^(BOOL userPressedOK, NSString *_Nullable phoneNumber) {
+    if (!userPressedOK || !phoneNumber.length) {
+      return;
+    }
+    completion(phoneNumber);
+  }];
+}
+
+/** @fn commonPhoneNumberInputWithLabel:Completion
+    @brief Finishes the phone number verification flow.
+    @param verificationID The verificationID from the backend.
+    @param verificationCode The verificationCode from the SMS message.
+ */
+- (void)commontPhoneVerificationWithVerificationID:(NSString *)verificationID
+                                  verificationCode:(NSString *)verificationCode {
+  [self showSpinner:^{
+    FIRAuthCredential *credential =
+        [[AppManager phoneAuthProvider] credentialWithVerificationID:verificationID
+                                                    verificationCode:verificationCode];
+    [[AppManager auth] signInWithCredential:credential
+                                 completion:^(FIRUser *_Nullable user,
+                                              NSError *_Nullable error) {
+      [self hideSpinner:^{
+        if (error) {
+          [self logFailure:@"failed to verify phone number" error:error];
+          [self showMessagePrompt:error.localizedDescription];
+          return;
+        }
+      }];
+    }];
+  }];
+}
+
 /** @fn updatePhoneNumber
     @brief Allows adding a verified phone number to the currently signed user.
  */
diff --git a/Example/Auth/Tests/FIRApp+FIRAuthUnitTests.m b/Example/Auth/Tests/FIRApp+FIRAuthUnitTests.m
index 7159452..b6d34bb 100644
--- a/Example/Auth/Tests/FIRApp+FIRAuthUnitTests.m
+++ b/Example/Auth/Tests/FIRApp+FIRAuthUnitTests.m
@@ -28,7 +28,8 @@
   return [[FIROptions alloc] initInternalWithOptionsDictionary:@{
     @"GOOGLE_APP_ID" : @"1:1085102361755:ios:f790a919483d5bdf",
     @"API_KEY" : @"FAKE_API_KEY",
-    @"GCM_SENDER_ID": @"217397612173"
+    @"GCM_SENDER_ID": @"217397612173",
+    @"CLIENT_ID" : @"123456.apps.googleusercontent.com",
   }];
 }
 
diff --git a/Example/Auth/Tests/FIRPhoneAuthProviderTests.m b/Example/Auth/Tests/FIRPhoneAuthProviderTests.m
index 9a0a219..5b29b02 100644
--- a/Example/Auth/Tests/FIRPhoneAuthProviderTests.m
+++ b/Example/Auth/Tests/FIRPhoneAuthProviderTests.m
@@ -20,6 +20,8 @@
 #import "FIRPhoneAuthProvider.h"
 #import "Phone/FIRPhoneAuthCredential_Internal.h"
 #import "Phone/NSString+FIRAuth.h"
+#import "FIRApp.h"
+#import "FIRApp+FIRAuthUnitTests.h"
 #import "FIRAuthAPNSToken.h"
 #import "FIRAuthAPNSTokenManager.h"
 #import "FIRAuthAppCredential.h"
@@ -30,14 +32,20 @@
 #import "FIRAuthErrorUtils.h"
 #import "FIRAuthGlobalWorkQueue.h"
 #import "FIRAuthBackend.h"
+#import "FIRAuthURLPresenter.h"
+#import "FIRGetProjectConfigRequest.h"
+#import "FIRGetProjectConfigResponse.h"
 #import "FIRSendVerificationCodeRequest.h"
 #import "FIRSendVerificationCodeResponse.h"
+#import "FIRAuthUIDelegate.h"
 #import "FIRVerifyClientRequest.h"
 #import "FIRVerifyClientResponse.h"
 #import "FIRApp+FIRAuthUnitTests.h"
 #import "OCMStubRecorder+FIRAuthUnitTests.h"
 #import <OCMock/OCMock.h>
 
+@import SafariServices;
+
 NS_ASSUME_NONNULL_BEGIN
 
 /** @var kTestPhoneNumber
@@ -75,12 +83,23 @@ static NSString *const kTestOldReceipt = @"old_receipt";
  */
 static NSString *const kTestOldSecret = @"old_secret";
 
-
 /** @var kTestVerificationCode
     @brief A fake verfication code.
  */
 static NSString *const kTestVerificationCode = @"verificationCode";
 
+/** @var kFakeReCAPTCHAToken
+    @brief A fake reCAPTCHA token.
+ */
+static NSString *const kFakeReCAPTCHAToken = @"fakeReCAPTCHAToken";
+
+/** @var kFakeRedirectURLStringFormat
+    @brief The format for a fake redirect URL string.
+ */
+static NSString *const kFakeRedirectURLStringWithoutReCAPTCHAToken = @"com.googleusercontent.apps.1"
+    "23456://firebaseauth/link?deep_link_id=https%3A%2F%2Fexample.firebaseapp.com%2F__%2Fauth%2Fcal"
+    "lback%3FauthType%3DverifyApp%26recaptchaToken%3D";
+
 /** @var kTestTimeout
     @brief A fake timeout value for waiting for push notification.
  */
@@ -141,6 +160,7 @@ static const NSTimeInterval kExpectationTimeout = 1;
   _mockNotificationManager = OCMClassMock([FIRAuthNotificationManager class]);
   OCMStub([_mockAuth notificationManager]).andReturn(_mockNotificationManager);
   _provider = [FIRPhoneAuthProvider providerWithAuth:_mockAuth];
+  OCMStub([_mockAuth authURLPresenter]).andReturn([FIRAuthURLPresenter new]);
 }
 
 - (void)tearDown {
@@ -248,6 +268,94 @@ static const NSTimeInterval kExpectationTimeout = 1;
   OCMVerifyAll(_mockAppCredentialManager);
 }
 
+/** @fn testVerifyPhoneNumberUIDelegate
+    @brief Tests a successful invocation of @c verifyPhoneNumber:UIDelegate:completion:.
+ */
+- (void)testVerifyPhoneNumberUIDelegate {
+  if ([SFSafariViewController class]) {
+    FIRApp *app = [FIRApp appForAuthUnitTestsWithName:@"testApp"];
+    OCMStub([_mockAuth app]).andReturn(app);
+    // Simulate missing app token error.
+    OCMExpect([_mockNotificationManager checkNotificationForwardingWithCallback:OCMOCK_ANY])
+        .andCallBlock1(^(FIRAuthNotificationForwardingCallback callback) { callback(YES); });
+    OCMExpect([_mockAppCredentialManager credential]).andReturn(nil);
+    OCMExpect([_mockAPNSTokenManager getTokenWithCallback:OCMOCK_ANY])
+        .andCallBlock1(^(FIRAuthAPNSTokenCallback callback) {
+      NSError *error = [NSError errorWithDomain:FIRAuthErrorDomain
+                                           code:FIRAuthErrorCodeMissingAppToken
+                                       userInfo:nil];
+      callback(nil, error);
+    });
+    OCMExpect([_mockBackend getProjectConfig:[OCMArg any] callback:[OCMArg any]])
+        .andCallBlock2(^(FIRGetProjectConfigRequest *request,
+                         FIRGetProjectConfigResponseCallback callback) {
+      XCTAssertNotNil(request);
+      dispatch_async(FIRAuthGlobalWorkQueue(), ^() {
+        id mockGetProjectConfigResponse = OCMClassMock([FIRGetProjectConfigResponse class]);
+        OCMStub([mockGetProjectConfigResponse authorizedDomains]).
+            andReturn(@[ @"test.firebaseapp.com"]);
+        callback(mockGetProjectConfigResponse, nil);
+      });
+    });
+    // Mock UIDelegate.
+    id mockUIDelegate = OCMProtocolMock(@protocol(FIRAuthUIDelegate));
+    // Expect view controller presentation by UIDelegate.
+    id presenterArg = [OCMArg isKindOfClass:[SFSafariViewController class]];
+    OCMExpect([mockUIDelegate presentViewController:presenterArg
+                                           animated:YES
+                                         completion:nil]).andDo(^(NSInvocation *invocation) {
+      __unsafe_unretained id unretainedArgument;
+      // Indices 0 and 1 indicate the hidden arguments self and _cmd.
+      // `presentViewController` is at index 2.
+      [invocation getArgument:&unretainedArgument atIndex:2];
+      SFSafariViewController *viewController = unretainedArgument;
+      XCTAssertEqual(viewController.delegate, [_mockAuth authURLPresenter]);
+      XCTAssertTrue([viewController isKindOfClass:[SFSafariViewController class]]);
+      NSMutableString *fakeRedirectURLString =
+          [NSMutableString stringWithString:kFakeRedirectURLStringWithoutReCAPTCHAToken];
+      [fakeRedirectURLString appendString:kFakeReCAPTCHAToken];
+      [[_mockAuth authURLPresenter] canHandleURL:[NSURL URLWithString:fakeRedirectURLString]];
+    });
+    // Expect view controller dismissal by UIDelegate.
+    OCMExpect([mockUIDelegate dismissViewControllerAnimated:OCMOCK_ANY completion:OCMOCK_ANY]).
+        andDo(^(NSInvocation *invocation) {
+      __unsafe_unretained id unretainedArgument;
+      // Indices 0 and 1 indicate the hidden arguments self and _cmd.
+      // `completion` is at index 3.
+      [invocation getArgument:&unretainedArgument atIndex:3];
+      void (^finishBlock)() = unretainedArgument;
+      finishBlock();
+    });
+
+    OCMExpect([_mockBackend sendVerificationCode:[OCMArg any] callback:[OCMArg any]])
+        .andCallBlock2(^(FIRSendVerificationCodeRequest *request,
+                         FIRSendVerificationCodeResponseCallback callback) {
+      XCTAssertEqualObjects(request.phoneNumber, kTestPhoneNumber);
+      XCTAssertNil(request.appCredential);
+      XCTAssertEqualObjects(request.reCAPTCHAToken, kFakeReCAPTCHAToken);
+      dispatch_async(FIRAuthGlobalWorkQueue(), ^() {
+        id mockSendVerificationCodeResponse = OCMClassMock([FIRSendVerificationCodeResponse class]);
+        OCMStub([mockSendVerificationCodeResponse verificationID]).andReturn(kTestVerificationID);
+        callback(mockSendVerificationCodeResponse, nil);
+      });
+    });
+
+    XCTestExpectation *expectation = [self expectationWithDescription:@"callback"];
+    [_provider verifyPhoneNumber:kTestPhoneNumber
+                      UIDelegate:mockUIDelegate
+                      completion:^(NSString *_Nullable verificationID, NSError *_Nullable error) {
+      XCTAssertTrue([NSThread isMainThread]);
+      XCTAssertNil(error);
+      XCTAssertEqualObjects(verificationID, kTestVerificationID);
+      XCTAssertEqualObjects(verificationID.fir_authPhoneNumber, kTestPhoneNumber);
+      [expectation fulfill];
+    }];
+    [self waitForExpectationsWithTimeout:kExpectationTimeout handler:nil];
+    OCMVerifyAll(_mockBackend);
+    OCMVerifyAll(_mockNotificationManager);
+  }
+}
+
 /** @fn testNotForwardingNotification
     @brief Tests returning an error for the app failing to forward notification.
  */
diff --git a/Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m b/Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m
index 4a0e7e7..1fe4d15 100644
--- a/Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m
+++ b/Firebase/Auth/Source/AuthProviders/Phone/FIRPhoneAuthProvider.m
@@ -19,22 +19,37 @@
 #import "FIRLogger.h"
 #import "FIRPhoneAuthCredential_Internal.h"
 #import "NSString+FIRAuth.h"
+#import "FIRApp.h"
 #import "FIRAuthAPNSToken.h"
 #import "FIRAuthAPNSTokenManager.h"
 #import "FIRAuthAppCredential.h"
 #import "FIRAuthAppCredentialManager.h"
 #import "FIRAuthGlobalWorkQueue.h"
 #import "FIRAuth_Internal.h"
+#import "FIRAuthURLPresenter.h"
 #import "FIRAuthNotificationManager.h"
 #import "FIRAuthErrorUtils.h"
 #import "FIRAuthBackend.h"
+#import "FirebaseAuthVersion.h"
+#import "FIROptions.h"
+#import "FIRGetProjectConfigRequest.h"
+#import "FIRGetProjectConfigResponse.h"
 #import "FIRSendVerificationCodeRequest.h"
 #import "FIRSendVerificationCodeResponse.h"
 #import "FIRVerifyClientRequest.h"
 #import "FIRVerifyClientResponse.h"
+#import <GoogleToolboxForMac/GTMNSDictionary+URLArguments.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
+/** @typedef FIRReCAPTCHAURLCallBack
+    @brief The callback invoked at the end of the flow to fetch a reCAPTCHA URL.
+    @param reCAPTCHAURL The reCAPTCHA URL.
+    @param error The error that occured while fetching the reCAPTCHAURL, if any.
+ */
+typedef void (^FIRReCAPTCHAURLCallBack)(NSURL *_Nullable reCAPTCHAURL,
+                                        NSError *_Nullable error);
+
 /** @typedef FIRVerifyClientCallback
     @brief The callback invoked at the end of a client verification flow.
     @param appCredential credential that proves the identity of the app during a phone
@@ -44,6 +59,28 @@ NS_ASSUME_NONNULL_BEGIN
 typedef void (^FIRVerifyClientCallback)(FIRAuthAppCredential *_Nullable appCredential,
                                         NSError *_Nullable error);
 
+/** @typedef FIRFetchAuthDomainCallback
+    @brief The callback invoked at the end of the flow to fetch the Auth domain.
+    @param authDomain The Auth domain.
+    @param error The error that occured while fetching the auth domain, if any.
+ */
+typedef void (^FIRFetchAuthDomainCallback)(NSString *_Nullable authDomain,
+                                           NSError *_Nullable error);
+/** @var kAuthDomainSuffix
+    @brief The suffix of the auth domain pertiaining to a given Firebase project.
+ */
+static NSString *const kAuthDomainSuffix = @"firebaseapp.com";
+
+/** @var kauthTypeVerifyApp
+    @brief The auth type to be specified in the app verification request.
+ */
+static NSString *const kAuthTypeVerifyApp = @"verifyApp";
+
+/** @var kReCAPTCHAURLStringFormat
+    @brief The format of the URL used to open the reCAPTCHA page during app verification.
+ */
+NSString *const kReCAPTCHAURLStringFormat = @"https://%@/__/auth/handler?%@";
+
 @implementation FIRPhoneAuthProvider {
 
   /** @var _auth
@@ -68,6 +105,21 @@ typedef void (^FIRVerifyClientCallback)(FIRAuthAppCredential *_Nullable appCrede
 - (void)verifyPhoneNumber:(NSString *)phoneNumber
                completion:(nullable FIRVerificationResultCallback)completion {
   dispatch_async(FIRAuthGlobalWorkQueue(), ^{
+    [self internalVerifyPhoneNumber:phoneNumber completion:^(NSString *_Nullable verificationID,
+                                                             NSError *_Nullable error) {
+      if (completion) {
+        dispatch_async(dispatch_get_main_queue(), ^{
+          completion(verificationID, error);
+        });
+      }
+    }];
+  });
+}
+
+- (void)verifyPhoneNumber:(NSString *)phoneNumber
+               UIDelegate:(nullable id<FIRAuthUIDelegate>)UIDelegate
+               completion:(nullable FIRVerificationResultCallback)completion {
+  dispatch_async(FIRAuthGlobalWorkQueue(), ^{
     FIRVerificationResultCallback callBackOnMainThread = ^(NSString *_Nullable verificationID,
                                                            NSError *_Nullable error) {
       if (completion) {
@@ -76,21 +128,59 @@ typedef void (^FIRVerifyClientCallback)(FIRAuthAppCredential *_Nullable appCrede
         });
       }
     };
-
-    if (!phoneNumber.length) {
-      callBackOnMainThread(nil,
-                           [FIRAuthErrorUtils missingPhoneNumberErrorWithMessage:nil]);
-      return;
-    }
-    [_auth.notificationManager checkNotificationForwardingWithCallback:
-        ^(BOOL isNotificationBeingForwarded) {
-      if (!isNotificationBeingForwarded) {
-        callBackOnMainThread(nil, [FIRAuthErrorUtils notificationNotForwardedError]);
+    [self internalVerifyPhoneNumber:phoneNumber completion:^(NSString *_Nullable verificationID,
+                                                             NSError *_Nullable error) {
+      if (!error) {
+        callBackOnMainThread(verificationID, nil);
         return;
       }
-      [self verifyClientAndSendVerificationCodeToPhoneNumber:phoneNumber
-                                 retryOnInvalidAppCredential:YES
-                                                    callback:callBackOnMainThread];
+      NSError *underlyingError = error.userInfo[NSUnderlyingErrorKey];
+      BOOL isInvalidAppCredential = error.code == FIRAuthErrorCodeInternalError &&
+          underlyingError.code == FIRAuthErrorCodeInvalidAppCredential;
+      if (error.code != FIRAuthErrorCodeMissingAppToken && !isInvalidAppCredential) {
+        completion(nil, error);
+        return;
+      }
+      [self reCAPTCHAURLWithCompletion:^(NSURL *_Nullable reCAPTCHAURL,
+                                         NSError *_Nullable error) {
+        if (error) {
+          callBackOnMainThread(nil, error);
+          return;
+        }
+        [_auth.authURLPresenter presentURL:reCAPTCHAURL
+                                UIDelegate:UIDelegate
+                           callbackMatcher:^BOOL(NSURL * _Nullable callbackURL) {
+                             return [self isVerifyAppURL:callbackURL];
+                           }
+                                completion:^(NSURL *_Nullable callbackURL,
+                                             NSError *_Nullable error) {
+          if (error) {
+            completion(nil, error);
+            return;
+          }
+          NSDictionary<NSString *, NSString *> *URLQueryItems =
+              [NSDictionary gtm_dictionaryWithHttpArgumentsString:callbackURL.query];;
+          URLQueryItems =
+              [NSDictionary gtm_dictionaryWithHttpArgumentsString:URLQueryItems[@"deep_link_id"]];
+          NSString *reCAPTCHA = URLQueryItems[@"recaptchaToken"];
+          FIRSendVerificationCodeRequest *request =
+            [[FIRSendVerificationCodeRequest alloc] initWithPhoneNumber:phoneNumber
+                                                          appCredential:nil
+                                                         reCAPTCHAToken:reCAPTCHA
+                                                   requestConfiguration:_auth.requestConfiguration];
+          [FIRAuthBackend sendVerificationCode:request
+                                      callback:^(FIRSendVerificationCodeResponse
+                                                 *_Nullable response, NSError *_Nullable error) {
+            if (error) {
+              callBackOnMainThread(nil, error);
+              return;
+            }
+            // Associate the phone number with the verification ID.
+            response.verificationID.fir_authPhoneNumber = phoneNumber;
+            callBackOnMainThread(response.verificationID, nil);
+          }];
+        }];
+      }];
     }];
   });
 }
@@ -111,6 +201,71 @@ typedef void (^FIRVerifyClientCallback)(FIRAuthAppCredential *_Nullable appCrede
 }
 
 #pragma mark - Internal Methods
+/** @fn isVerifyAppURL:
+    @brief Parses a URL into all available query items.
+    @param URL The url to be checked against the authType string.
+    @return Whether or not the URL matches authType.
+ */
+- (BOOL)isVerifyAppURL:(nullable NSURL *)URL {
+  if (!URL) {
+    return NO;
+  }
+  NSURLComponents *actualURLComponents =
+      [NSURLComponents componentsWithURL:URL resolvingAgainstBaseURL:NO];
+  actualURLComponents.query = nil;
+  actualURLComponents.fragment = nil;
+
+  NSURLComponents *expectedURLComponents = [NSURLComponents new];
+  NSArray *strings = [_auth.app.options.clientID componentsSeparatedByString:@"."];
+  expectedURLComponents.scheme =
+      [[strings reverseObjectEnumerator].allObjects componentsJoinedByString:@"."];
+  expectedURLComponents.host = @"firebaseauth";
+  expectedURLComponents.path = @"/link";
+
+  if (!([[expectedURLComponents URL] isEqual:[actualURLComponents URL]])) {
+    return NO;
+  }
+  NSDictionary<NSString *, NSString *> *URLQueryItems =
+      [NSDictionary gtm_dictionaryWithHttpArgumentsString:URL.query];
+  NSURL *deeplinkURL = [NSURL URLWithString:URLQueryItems[@"deep_link_id"]];
+  NSDictionary<NSString *, NSString *> *deeplinkQueryItems =
+      [NSDictionary gtm_dictionaryWithHttpArgumentsString:deeplinkURL.query];
+  if ([deeplinkQueryItems[@"authType"] isEqualToString:kAuthTypeVerifyApp]) {
+    return YES;
+  }
+  return NO;
+}
+
+/** @fn internalVerifyPhoneNumber:completion:
+    @brief Starts the phone number authentication flow by sending a verifcation code to the
+        specified phone number.
+    @param phoneNumber The phone number to be verified.
+    @param completion The callback to be invoked when the verification flow is finished.
+ */
+
+- (void)internalVerifyPhoneNumber:(NSString *)phoneNumber
+                       completion:(nullable FIRVerificationResultCallback)completion {
+  if (!phoneNumber.length) {
+    completion(nil, [FIRAuthErrorUtils missingPhoneNumberErrorWithMessage:nil]);
+    return;
+  }
+  [_auth.notificationManager checkNotificationForwardingWithCallback:
+      ^(BOOL isNotificationBeingForwarded) {
+    if (!isNotificationBeingForwarded) {
+      completion(nil, [FIRAuthErrorUtils notificationNotForwardedError]);
+      return;
+    }
+    FIRVerificationResultCallback callback = ^(NSString *_Nullable verificationID,
+                                               NSError *_Nullable error) {
+      if (completion) {
+        completion(verificationID, error);
+      }
+    };
+    [self verifyClientAndSendVerificationCodeToPhoneNumber:phoneNumber
+                               retryOnInvalidAppCredential:YES
+                                                  callback:callback];
+  }];
+}
 
 /** @fn verifyClientAndSendVerificationCodeToPhoneNumber:retryOnInvalidAppCredential:callback:
     @brief Starts the flow to verify the client via silent push notification.
@@ -201,6 +356,62 @@ typedef void (^FIRVerifyClientCallback)(FIRAuthAppCredential *_Nullable appCrede
   }];
 }
 
+- (void)reCAPTCHAURLWithCompletion:(FIRReCAPTCHAURLCallBack)completion {
+  [self fetchAuthDomainWithCompletion:^(NSString *_Nullable authDomain,
+                                        NSError *_Nullable error) {
+    if (error) {
+      completion(nil, error);
+      return;
+    }
+    NSString *bundleID = [NSBundle mainBundle].bundleIdentifier;
+    NSString *clienID = _auth.app.options.clientID;
+    NSString *apiKey = _auth.app.options.APIKey;
+    NSMutableDictionary *urlArguments = [[NSMutableDictionary alloc] initWithDictionary: @{
+      @"apiKey" : apiKey,
+      @"authType" : kAuthTypeVerifyApp,
+      @"ibi" : bundleID,
+      @"clientId" : clienID,
+      @"v" : [FIRAuthBackend authUserAgent]
+    }];
+    if (_auth.requestConfiguration.languageCode) {
+      urlArguments[@"hl"] = _auth.requestConfiguration.languageCode;
+    }
+    NSString *argumentsString = [urlArguments gtm_httpArgumentsString];
+    NSString *URLString =
+        [NSString stringWithFormat:kReCAPTCHAURLStringFormat, authDomain, argumentsString];
+    completion([NSURL URLWithString:URLString], nil);
+  }];
+}
+
+- (void)fetchAuthDomainWithCompletion:(FIRFetchAuthDomainCallback)completion {
+  FIRGetProjectConfigRequest *request =
+      [[FIRGetProjectConfigRequest alloc] initWithRequestConfiguration:_auth.requestConfiguration];
+
+  [FIRAuthBackend getProjectConfig:request
+                          callback:^(FIRGetProjectConfigResponse *_Nullable response,
+                                     NSError *_Nullable error) {
+    if (error) {
+      completion(nil, error);
+      return;
+    }
+    NSString *authDomain;
+    for (NSString *domain in response.authorizedDomains) {
+      NSInteger index = domain.length - kAuthDomainSuffix.length;
+      if (index >= 2) {
+        if ([domain hasSuffix:kAuthDomainSuffix] && domain.length >= kAuthDomainSuffix.length + 2) {
+          authDomain = domain;
+          break;
+        }
+      }
+    }
+    if (!authDomain.length) {
+      completion(nil, [FIRAuthErrorUtils unexpectedErrorResponseWithDeserializedResponse:response]);
+      return;
+    }
+    completion(authDomain, nil);
+  }];
+}
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/Firebase/Auth/Source/FIRAuth.m b/Firebase/Auth/Source/FIRAuth.m
index d2915a3..dd0b0bf 100644
--- a/Firebase/Auth/Source/FIRAuth.m
+++ b/Firebase/Auth/Source/FIRAuth.m
@@ -64,6 +64,7 @@
 #import "FIRAuthAppDelegateProxy.h"
 #import "AuthProviders/Phone/FIRPhoneAuthCredential_Internal.h"
 #import "FIRAuthNotificationManager.h"
+#import "FIRAuthURLPresenter.h"
 #endif
 
 #pragma mark - Constants
@@ -387,6 +388,9 @@ static NSMutableDictionary *gKeychainServiceNameForAppName;
       });
       return uid;
     };
+    #if TARGET_OS_IOS
+    _authURLPresenter = [[FIRAuthURLPresenter alloc] init];
+    #endif
   }
   return self;
 }
@@ -984,11 +988,15 @@ static NSMutableDictionary *gKeychainServiceNameForAppName;
   });
   return result;
 }
-#endif
 
-- (BOOL)canHandleURL:(NSURL *)url {
-  return NO;
+- (BOOL)canHandleURL:(NSURL *)URL {
+  __block BOOL result = NO;
+  dispatch_sync(FIRAuthGlobalWorkQueue(), ^{
+    result = [_authURLPresenter canHandleURL:URL];
+  });
+  return result;
 }
+#endif
 
 #pragma mark - Internal Methods
 
diff --git a/Firebase/Auth/Source/FIRAuthURLPresenter.m b/Firebase/Auth/Source/FIRAuthURLPresenter.m
index 90ceed6..fc84383 100644
--- a/Firebase/Auth/Source/FIRAuthURLPresenter.m
+++ b/Firebase/Auth/Source/FIRAuthURLPresenter.m
@@ -68,7 +68,7 @@ NS_ASSUME_NONNULL_BEGIN
 }
 
 - (BOOL)canHandleURL:(NSURL *)URL {
-  if (_callbackMatcher(URL)) {
+  if (_callbackMatcher && _callbackMatcher(URL)) {
     _callbackMatcher = nil;
     [self finishPresentationWithURL:URL error:nil];
     return YES;
diff --git a/Firebase/Auth/Source/FIRAuth_Internal.h b/Firebase/Auth/Source/FIRAuth_Internal.h
index d568d45..a89ebf9 100644
--- a/Firebase/Auth/Source/FIRAuth_Internal.h
+++ b/Firebase/Auth/Source/FIRAuth_Internal.h
@@ -24,12 +24,20 @@
 @class FIRAuthAPNSTokenManager;
 @class FIRAuthAppCredentialManager;
 @class FIRAuthNotificationManager;
+@class FIRAuthURLPresenter;
 #endif
 
 NS_ASSUME_NONNULL_BEGIN
 
 @interface FIRAuth ()
 
+#if TARGET_OS_IOS
+/** @property authURLPresenter
+    @brief An object that takes care of presenting URLs via the auth instance.
+ */
+@property(nonatomic, strong, readonly) FIRAuthURLPresenter *authURLPresenter;
+#endif
+
 /** @property requestConfiguration
     @brief The configuration object comprising of paramters needed to make a request to Firebase
         Auth's backend.
diff --git a/Firebase/Auth/Source/Public/FIRAuth.h b/Firebase/Auth/Source/Public/FIRAuth.h
index ad6b635..eeb7ff9 100644
--- a/Firebase/Auth/Source/Public/FIRAuth.h
+++ b/Firebase/Auth/Source/Public/FIRAuth.h
@@ -280,6 +280,18 @@ FIR_SWIFT_NAME(Auth)
  */
 - (instancetype)init NS_UNAVAILABLE;
 
+/** @fn canHandleURL:
+    @brief Whether the specific URL is handled by @c FIRAuth .
+    @param URL The URL received by the application delegate from any of the openURL method.
+    @return Whether or the URL is handled. YES means the URL is for Firebase Auth
+        so the caller should ignore the URL from further processing, and NO means the
+        the URL is for the app (or another libaray) so the caller should continue handling
+        this URL as usual.
+    @remarks If swizzling is disabled, URLs received by the application delegate must be forwarded
+        to this method for phone number auth to work.
+ */
+- (BOOL)canHandleURL:(nonnull NSURL *)URL;
+
 /** @fn fetchProvidersForEmail:completion:
     @brief Fetches the list of IdPs that can be used for signing in with the provided email address.
         Useful for an "identifier-first" sign-in flow.
diff --git a/Firebase/Auth/Source/Public/FIRPhoneAuthProvider.h b/Firebase/Auth/Source/Public/FIRPhoneAuthProvider.h
index 138028a..5acc500 100644
--- a/Firebase/Auth/Source/Public/FIRPhoneAuthProvider.h
+++ b/Firebase/Auth/Source/Public/FIRPhoneAuthProvider.h
@@ -20,6 +20,7 @@
 
 @class FIRAuth;
 @class FIRPhoneAuthCredential;
+@protocol FIRAuthUIDelegate;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -85,6 +86,29 @@ FIR_SWIFT_NAME(PhoneAuthProvider)
 - (void)verifyPhoneNumber:(NSString *)phoneNumber
                completion:(nullable FIRVerificationResultCallback)completion;
 
+/** @fn verifyPhoneNumber:UIDelegate:completion:
+    @brief Starts the phone number authentication flow by sending a verifcation code to the
+        specified phone number.
+    @param phoneNumber The phone number to be verified.
+    @param UIDelegate A view controller object used to present the SFSafariViewController or
+        WKWebview.
+    @param completion The callback to be invoked when the verification flow is finished.
+    @remarks Possible error codes:
+    <ul>
+        <li>@c FIRAuthErrorCodeCaptchaCheckFailed - Indicates that the reCAPTCHA token obtained by
+            the Firebase Auth is invalid or has expired.</li>
+        <li>@c FIRAuthErrorCodeQuotaExceeded - Indicates that the phone verification quota for this
+            project has been exceeded.</li>
+        <li>@c FIRAuthErrorCodeInvalidPhoneNumber - Indicates that the phone number provided is
+            invalid.</li>
+        <li>@c FIRAuthErrorCodeMissingPhoneNumber - Indicates that a phone number was not provided.
+        </li>
+    </ul>
+ */
+- (void)verifyPhoneNumber:(NSString *)phoneNumber
+               UIDelegate:(nullable id<FIRAuthUIDelegate>)UIDelegate
+               completion:(nullable FIRVerificationResultCallback)completion;
+
 /** @fn credentialWithVerificationID:verificationCode:
     @brief Creates an @c FIRAuthCredential for the phone number provider identified by the
         verification ID and verification code.
diff --git a/Firebase/Auth/Source/RPCs/FIRAuthBackend.h b/Firebase/Auth/Source/RPCs/FIRAuthBackend.h
index 65f93ce..a82c3a7 100644
--- a/Firebase/Auth/Source/RPCs/FIRAuthBackend.h
+++ b/Firebase/Auth/Source/RPCs/FIRAuthBackend.h
@@ -210,6 +210,12 @@ typedef void (^FIRVerifyClientResponseCallback)
  */
 @interface FIRAuthBackend : NSObject
 
+/** @fn authUserAgent
+    @brief Retrieves the Firebase Auth user agent.
+    @return The Firebase Auth user agent.
+ */
++ (NSString *)authUserAgent;
+
 /** @fn setBackendImplementation:
     @brief Changes the default backend implementation to something else.
     @param backendImplementation The backend implementation to use.
diff --git a/Firebase/Auth/Source/RPCs/FIRAuthBackend.m b/Firebase/Auth/Source/RPCs/FIRAuthBackend.m
index afe05bd..2a70a80 100644
--- a/Firebase/Auth/Source/RPCs/FIRAuthBackend.m
+++ b/Firebase/Auth/Source/RPCs/FIRAuthBackend.m
@@ -465,6 +465,11 @@ static id<FIRAuthBackendImplementation> gBackendImplementation;
   [[self implementation] resetPassword:request callback:callback];
 }
 
++ (NSString *)authUserAgent {
+  return [NSString stringWithFormat:@"FirebaseAuth.iOS/%s %@",
+      FirebaseAuthVersionString, GTMFetcherStandardUserAgentString(nil)];
+}
+
 @end
 
 @interface FIRAuthBackendRPCIssuerImplementation : NSObject <FIRAuthBackendRPCIssuer>
@@ -480,8 +485,7 @@ static id<FIRAuthBackendImplementation> gBackendImplementation;
   self = [super init];
   if (self) {
     _fetcherService = [[GTMSessionFetcherService alloc] init];
-    _fetcherService.userAgent = [NSString stringWithFormat:@"FirebaseAuth.iOS/%s %@",
-        FirebaseAuthVersionString, GTMFetcherStandardUserAgentString(nil)];
+    _fetcherService.userAgent = [FIRAuthBackend authUserAgent];
     _fetcherService.callbackQueue = FIRAuthGlobalWorkQueue();
   }
   return self;