[Auth] Add app ID prefix to sample plist

[ncooke3]

+++ b/FirebaseAuth/Tests/SampleSwift/AuthenticationExample/SwiftApplication.plist
@@ -2,6 +2,8 @@
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <dict>
+       <key>AppIdentifierPrefix</key>
+       <string>$(AppIdentifierPrefix)</string>

Will enable you to easily test keychain groups without further configuring the sample app. This should dynamically evaluate to TEAMID.com.google.firebase.auth.keychainGroup1, but I did notice very sneaky behavior where the cert's team ID is not used as the app ID prefix for simulator builds. This caused the missing entitlements -34018 error when testing because kecyhain group I was looking for was not the same as the keychain group the app had provisioned on simulator. Using the $(AppIdentifierPrefix) variable as opposed to hardcoding something will ensure it's always what Xcode is looking for.

firebase-ios-sdk/FirebaseAuth/Tests/SampleSwift/AuthenticationExample/ViewControllers/SettingsViewController.swift

Lines 115 to 125 in 60b6dd5

	private func toggleAccessGroup() {
	if AppManager.shared.auth().userAccessGroup == nil {
	guard let bundleDictionary = Bundle.main.infoDictionary,
	let group = bundleDictionary["AppIdentifierPrefix"] as? String else {
	fatalError("Configure AppIdentifierPrefix in the plist")
	}
	AppManager.shared.auth().userAccessGroup = group + "com.google.firebase.auth.keychainGroup1"
	} else {
	AppManager.shared.auth().userAccessGroup = nil
	}
	}

#no-changelog