Issue title: Not able to build iOS app due to pod install failure on AppAuth 1.4.0 branch not found
 Issue body: ## Bug report

**Describe the bug**
I recently upgraded all my libraries to the latest major version using flutter pub upgrade --major-versions
Android version works without any issues however when I try to build for iOS I get an error on pod install related to AppAuth version 1.4.0. I don't have a direct reference to this so I assume it is related to the firebase dependencies. 

### Steps to reproduce

Steps to reproduce the behavior:

Every time when I either run pod install or flutter build ios
Note: I have deleted the ~/.cocoapods/repos folder but this has not fixed the issue.
I have tried to clone appAuth manually but it only works when the branch version is replaced with master instead of the version number (1.4.0) in this case. I can not find any reference to this link so I don't know where to update this link.
I have also left a message on the AppAuth GitHub but have not received a response yet.

the error: after running pod install:

Analyzing dependencies
cloud_firestore: Using Firebase SDK version '7.11.0' defined in 'firebase_core'
firebase_core: Using Firebase SDK version '7.11.0' defined in 'firebase_core'
firebase_messaging: Using Firebase SDK version '7.11.0' defined in 'firebase_core'
Downloading dependencies
Installing AppAuth (1.4.0)

[!] Error installing AppAuth
[!] /usr/local/bin/git clone https://github.com/openid/AppAuth-iOS.git /var/folders/0d/z_y7jpq177gbzb76f_yrpgy80000gn/T/d20210518-13343-uh97en --template= --single-branch --depth 1 --branch 1.4.0

Cloning into '/var/folders/0d/z_y7jpq177gbzb76f_yrpgy80000gn/T/d20210518-13343-uh97en'...
warning: Could not find remote branch 1.4.0 to clone.
fatal: Remote branch 1.4.0 not found in upstream origin

### Expected behavior

Expected to install the dependencies and be able to build my app.

### Sample project

---

## Additional context


---

### Flutter doctor

Run `flutter doctor` and paste the output below:

<details><summary>Click To Expand</summary>
[✓] Flutter (Channel stable, 2.0.6, on macOS 11.3.1 20E241 darwin-x64, locale en-AU)
    • Flutter version 2.0.6 at /Users/ray/Downloads/flutter
    • Framework revision 1d9032c7e1 (3 weeks ago), 2021-04-29 17:37:58 -0700
    • Engine revision 05e680e202
    • Dart version 2.12.3

[!] Android toolchain - develop for Android devices (Android SDK version 30.0.1)
    • Android SDK at /Users/ray/Library/Android/sdk
    • Platform android-30, build-tools 30.0.1
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.8+10-b944.6916264)
    ✗ Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/macos#android-setup for more details.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.4, Build version 12D4e
    • CocoaPods version 1.10.1

[✗] Chrome - develop for the web (Cannot find Chrome executable at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome)
    ! Cannot find Chrome. Try setting CHROME_EXECUTABLE to a Chrome executable.

[✓] Android Studio (version 4.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.8+10-b944.6916264)

[✓] VS Code (version 1.47.3)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.13.1

[!] Connected device
    ! No devices available
</details>

---

### Flutter dependencies

Run `flutter pub deps -- --style=compact` and paste the output below:

<details><summary>Click To Expand</summary>
Dart SDK 2.12.3
Flutter SDK 2.0.6
bog_mobile_app 1.9.8+201

dependencies:
- after_layout 1.1.0 [flutter]
- analyzer 1.5.0 [_fe_analyzer_shared cli_util collection convert crypto glob meta package_config path pub_semver source_span watcher yaml pedantic]
- auto_size_text 2.1.0 [flutter]
- cached_network_image 3.0.0 [flutter flutter_cache_manager octo_image]
- cloud_firestore 2.1.0 [cloud_firestore_platform_interface cloud_firestore_web firebase_core firebase_core_platform_interface flutter meta]
- connectivity 3.0.3 [flutter meta connectivity_platform_interface connectivity_macos connectivity_for_web]
- cupertino_icons 1.0.3
- datetime_picker_formfield 2.0.0 [flutter intl]
- device_info 2.0.0 [flutter device_info_platform_interface]
- dio 4.0.0 [http_parser path]
- dropdown_menu 1.1.1 [flutter]
- firebase_core 1.1.1 [firebase_core_platform_interface firebase_core_web flutter meta]
- firebase_messaging 9.1.4 [firebase_core firebase_core_platform_interface firebase_messaging_platform_interface firebase_messaging_web flutter meta]
- flushbar 1.10.4 [flutter]
- flutter 0.0.0 [characters collection meta typed_data vector_math sky_engine]
- flutter_cache_manager 3.0.2 [clock collection file flutter http image path path_provider pedantic rxdart sqflite uuid]
- flutter_colorpicker 0.4.0 [flutter]
- flutter_google_places 0.3.0 [flutter google_api_headers google_maps_webservice http rxdart]
- flutter_launcher_icons 0.9.0 [args image path yaml]
- flutter_markdown 0.6.2 [flutter markdown meta path]
- flutter_offline 2.0.0 [flutter connectivity wifi_info_flutter]
- flutter_secure_storage 4.2.0 [meta flutter]
- flutter_sms 2.3.1 [flutter flutter_web_plugins plugin_platform_interface url_launcher]
- flutter_spinkit 5.0.0 [flutter]
- font_awesome_flutter 9.0.0 [flutter]
- geocoding 2.0.0 [flutter geocoding_platform_interface]
- geolocator 7.0.3 [flutter geolocator_platform_interface geolocator_web]
- get_it 7.1.3 [async collection]
- google_sign_in 5.0.3 [google_sign_in_platform_interface google_sign_in_web flutter meta]
- hive 2.0.4 [meta crypto]
- hive_flutter 1.0.0 [flutter hive path_provider path]
- html 0.15.0 [csslib source_span]
- html2md 1.2.1 [html collection]
- html_unescape 2.0.0
- http 0.13.3 [async http_parser meta path pedantic]
- image_picker 0.7.5 [flutter flutter_plugin_android_lifecycle image_picker_platform_interface image_picker_for_web]
- intl 0.17.0 [clock path]
- local_auth 1.1.5 [flutter meta intl platform flutter_plugin_android_lifecycle]
- location 4.1.1 [flutter location_platform_interface location_web meta]
- mime 1.0.0
- open_file 3.2.1 [flutter ffi]
- path_provider 2.0.1 [flutter path_provider_platform_interface path_provider_macos path_provider_linux path_provider_windows]
- permission 0.1.7 [flutter]
- permission_handler 7.1.0 [flutter meta permission_handler_platform_interface]
- prefs 3.3.0 [flutter shared_preferences shared_preferences_web]
- progress_hud 1.1.0 [flutter]
- provider 5.0.0 [collection flutter nested]
- sentry_flutter 5.0.0 [flutter flutter_web_plugins sentry package_info_plus]
- shared_preferences 2.0.5 [meta flutter shared_preferences_platform_interface shared_preferences_linux shared_preferences_macos shared_preferences_web shared_preferences_windows]
- sqflite 2.0.0+3 [flutter sqflite_common path]
- sticky_headers 0.2.0 [flutter]
- super_tooltip 1.0.1 [flutter]
- uni_links 0.5.1 [flutter uni_links_platform_interface uni_links_web]
- url_launcher 6.0.3 [flutter url_launcher_platform_interface url_launcher_linux url_launcher_macos url_launcher_windows url_launcher_web]

dev dependencies:
- build_runner 2.0.3 [args async analyzer build build_config build_daemon build_resolvers build_runner_core code_builder collection crypto dart_style frontend_server_client glob graphs http_multi_server io js logging meta mime package_config path pedantic pool pub_semver pubspec_parse shelf shelf_web_socket stack_trace stream_transform timing watcher web_socket_channel yaml]

transitive dependencies:
- _fe_analyzer_shared 21.0.0 [meta]
- archive 3.1.2 [crypto path]
- args 2.0.0
- async 2.6.1 [meta collection]
- build 2.0.1 [analyzer async convert crypto glob logging meta path]
- build_config 1.0.0 [checked_yaml json_annotation path pubspec_parse yaml]
- build_daemon 3.0.0 [built_collection built_value http_multi_server logging pedantic path pool shelf shelf_web_socket stream_transform watcher web_socket_channel]
- build_resolvers 2.0.1 [analyzer build crypto graphs logging path package_config pool pub_semver stream_transform]
- build_runner_core 7.0.0 [async build build_config build_resolvers collection convert crypto glob graphs json_annotation logging meta path package_config pedantic pool timing watcher yaml]
- built_collection 5.0.0
- built_value 8.0.6 [built_collection collection fixnum]
- characters 1.1.0
- charcode 1.2.0
- checked_yaml 2.0.1 [json_annotation source_span yaml]
- cli_util 0.3.0 [meta path]
- clock 1.1.0
- cloud_firestore_platform_interface 5.0.1 [collection firebase_core flutter meta plugin_platform_interface]
- cloud_firestore_web 2.0.1 [cloud_firestore_platform_interface firebase_core firebase_core_web flutter flutter_web_plugins js]
- code_builder 4.0.0 [built_collection built_value collection matcher meta]
- collection 1.15.0
- connectivity_for_web 0.4.0 [connectivity_platform_interface flutter_web_plugins flutter]
- connectivity_macos 0.2.0 [flutter]
- connectivity_platform_interface 2.0.1 [flutter meta plugin_platform_interface]
- convert 3.0.0 [typed_data]
- crypto 3.0.1 [collection typed_data]
- csslib 0.17.0 [source_span]
- dart_style 2.0.1 [analyzer args path pub_semver source_span]
- device_info_platform_interface 2.0.1 [flutter meta plugin_platform_interface]
- ffi 1.0.0
- file 6.1.1 [meta path]
- firebase_core_platform_interface 4.0.1 [collection flutter meta plugin_platform_interface]
- firebase_core_web 1.0.3 [firebase_core_platform_interface flutter flutter_web_plugins js meta]
- firebase_messaging_platform_interface 2.1.4 [firebase_core flutter meta plugin_platform_interface]
- firebase_messaging_web 1.0.7 [firebase_core firebase_core_web firebase_messaging_platform_interface flutter flutter_web_plugins js meta]
- fixnum 1.0.0
- flutter_blurhash 0.6.0 [flutter meta pedantic]
- flutter_plugin_android_lifecycle 2.0.1 [flutter]
- flutter_web_plugins 0.0.0 [flutter js characters collection meta typed_data vector_math]
- frontend_server_client 2.1.0 [async path]
- geocoding_platform_interface 2.0.0 [flutter meta plugin_platform_interface]
- geolocator_platform_interface 2.0.2 [flutter plugin_platform_interface vector_math meta]
- geolocator_web 2.0.3 [flutter flutter_web_plugins geolocator_platform_interface]
- glob 2.0.1 [async collection file path pedantic string_scanner]
- google_api_headers 1.0.0 [flutter package_info]
- google_maps_webservice 0.0.20-nullsafety.5 [http meta json_annotation]
- google_sign_in_platform_interface 2.0.1 [flutter meta quiver]
- google_sign_in_web 0.10.0 [google_sign_in_platform_interface flutter flutter_web_plugins meta js]
- graphs 2.0.0
- http_multi_server 3.0.1 [async]
- http_parser 4.0.0 [charcode collection source_span string_scanner typed_data]
- image 3.0.2 [archive meta xml]
- image_picker_for_web 2.0.0 [image_picker_platform_interface meta flutter flutter_web_plugins]
- image_picker_platform_interface 2.1.0 [flutter meta http plugin_platform_interface]
- io 1.0.0 [meta path string_scanner]
- js 0.6.3
- json_annotation 4.0.1
- location_platform_interface 2.1.0 [flutter meta plugin_platform_interface]
- location_web 3.0.0 [flutter flutter_web_plugins http_parser js location_platform_interface meta]
- logging 1.0.1
- markdown 4.0.0 [args charcode meta]
- matcher 0.12.10 [stack_trace]
- meta 1.3.0
- nested 1.0.0 [flutter]
- octo_image 1.0.0+1 [flutter flutter_blurhash]
- package_config 2.0.0 [path]
- package_info 2.0.0 [flutter]
- package_info_plus 1.0.1 [flutter package_info_plus_platform_interface package_info_plus_linux package_info_plus_macos package_info_plus_windows package_info_plus_web]
- package_info_plus_linux 1.0.1 [package_info_plus_platform_interface flutter path]
- package_info_plus_macos 1.1.1 [flutter]
- package_info_plus_platform_interface 1.0.1 [flutter meta plugin_platform_interface]
- package_info_plus_web 1.0.1 [http package_info_plus_platform_interface flutter flutter_web_plugins meta]
- package_info_plus_windows 1.0.1 [package_info_plus_platform_interface ffi flutter win32]
- path 1.8.0
- path_provider_linux 2.0.0 [path xdg_directories path_provider_platform_interface flutter]
- path_provider_macos 2.0.0 [flutter]
- path_provider_platform_interface 2.0.1 [flutter meta platform plugin_platform_interface]
- path_provider_windows 2.0.1 [path_provider_platform_interface meta path flutter ffi win32]
- pedantic 1.11.0
- permission_handler_platform_interface 3.3.0 [flutter meta plugin_platform_interface]
- petitparser 4.1.0 [meta]
- platform 3.0.0
- plugin_platform_interface 2.0.0 [meta]
- pool 1.5.0 [async stack_trace]
- process 4.2.1 [file path platform]
- pub_semver 2.0.0 [collection]
- pubspec_parse 1.0.0 [checked_yaml collection json_annotation pub_semver yaml]
- quiver 3.0.1 [matcher]
- rxdart 0.26.0
- sentry 5.0.0 [http meta stack_trace uuid]
- shared_preferences_linux 2.0.0 [flutter file meta path path_provider_linux shared_preferences_platform_interface]
- shared_preferences_macos 2.0.0 [shared_preferences_platform_interface flutter]
- shared_preferences_platform_interface 2.0.0 [flutter]
- shared_preferences_web 2.0.0 [shared_preferences_platform_interface flutter flutter_web_plugins meta]
- shared_preferences_windows 2.0.0 [shared_preferences_platform_interface flutter file meta path path_provider_platform_interface path_provider_windows]
- shelf 1.1.4 [async collection http_parser path stack_trace stream_channel]
- shelf_web_socket 1.0.1 [shelf stream_channel web_socket_channel]
- sky_engine 0.0.99
- source_span 1.8.1 [collection path term_glyph]
- sqflite_common 2.0.0+2 [synchronized path meta]
- stack_trace 1.10.0 [path]
- stream_channel 2.1.0 [async]
- stream_transform 2.0.0
- string_scanner 1.1.0 [charcode source_span]
- synchronized 3.0.0
- term_glyph 1.2.0
- timing 1.0.0 [json_annotation]
- typed_data 1.3.0 [collection]
- uni_links_platform_interface 1.0.0 [flutter plugin_platform_interface]
- uni_links_web 0.1.0 [flutter flutter_web_plugins uni_links_platform_interface]
- url_launcher_linux 2.0.0 [flutter]
- url_launcher_macos 2.0.0 [flutter]
- url_launcher_platform_interface 2.0.2 [flutter plugin_platform_interface]
- url_launcher_web 2.0.0 [url_launcher_platform_interface meta flutter flutter_web_plugins]
- url_launcher_windows 2.0.0 [flutter]
- uuid 3.0.4 [crypto]
- vector_math 2.1.0
- watcher 1.0.0 [async path pedantic]
- web_socket_channel 2.1.0 [async crypto stream_channel]
- wifi_info_flutter 2.0.0 [flutter wifi_info_flutter_platform_interface]
- wifi_info_flutter_platform_interface 2.0.1 [plugin_platform_interface flutter]
- win32 2.0.5 [ffi]
- xdg_directories 0.2.0 [meta path process]
- xml 5.1.0 [collection meta petitparser]
- yaml 3.1.0 [collection source_span string_scanner]

</details>

---

 Comments: 
 Comment 0: Hi @raykleijngeld 
I'm pretty sure AppAuth is an iOS native library for OAuth. Not sure what this has to do with firebase in any way?
Are you importing it in your Podfile?

Either way, this doesn't really look like a FlutterFire issue.
Thank you
{'source': 'GithubIssues', 'repo_name_with_owner': 'FirebaseExtended/flutterfire', 'issue_id': 893862779, 'repo_stars': 6677.0}