FIRAuthDataResult
@interface FIRAuthDataResult : NSObjectHelper object that contains the result of a successful sign-in, link and reauthenticate
    action. It contains references to a User instance and a AdditionalUserInfo instance.
- 
                  
                  This class should not be initialized manually. AuthDataResultinstance is returned as part ofAuthDataResultCallback.DeclarationObjective-C - (nonnull instancetype)init;
- 
                  
                  The signed in user. DeclarationObjective-C @property (nonatomic, readonly) FIRUser *_Nonnull user;
- 
                  
                  If available contains the additional IdP specific information about signed in user. DeclarationObjective-C @property (nonatomic, readonly, nullable) FIRAdditionalUserInfo *additionalUserInfo;
- 
                  
                  This property will be non-nil after a successful headful-lite sign-in via signIn(with:uiDelegate:completion:). May be used to obtain the accessToken and/or IDToken pertaining to a recently signed-in user.DeclarationObjective-C @property (nonatomic, readonly, nullable) FIRAuthCredential *credential;