Access Google APIs in an iOS app
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AI-generated Key Takeaways
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To access Google services APIs like Drive and Gmail, apps need user consent and access tokens, typically obtained through OAuth 2.0 client flows, which the Google Sign-In library can implement for you.
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Before making a Google API call, check the
grantedScopesproperty ofGIDGoogleUserto see which permissions your app already has. -
If your app needs additional permissions for a specific interaction, use
addScopes:presentingViewController:completionoraddScopes:presentingWindow:completionto request them from the user. -
To ensure your Google API calls use valid access tokens, wrap them in a
refreshTokensIfNeededWithCompletion:block to handle token expiration and renewal. -
You can use the refreshed access token by including it in the header of a REST or gRPC request or by utilizing the fetcher authorizer with the Google APIs Client Library.
Some Google services, such as Drive, Gmail, and many others, provide public APIs that you can use to create apps that help users work with their data in these services. To access these services, apps must implement one of the OAuth 2.0 client flows to get consent from users and obtain access tokens, which grant access to the APIs.
You can use the Google Sign-In library, which implements the OAuth 2.0 flow for you, to get access tokens for the signed-in user.
Before you begin
You must complete the basic Google Sign-In integration.
1. Check which scopes have been granted
Before you make a call to a Google API, check which scopes have already been
granted to your app, using the grantedScopes property of GIDGoogleUser:
Swift
letdriveScope="https://www.googleapis.com/auth/drive.readonly"
letgrantedScopes=user.grantedScopes
ifgrantedScopes==nil||!grantedScopes!.contains(driveScope){
// Request additional Drive scope.
}
Objective-C
NSString*driveScope=@"https://www.googleapis.com/auth/drive.readonly";
// Check if the user has granted the Drive scope
if(![user.grantedScopescontainsObject:driveScope]){
// request additional drive scope
}
Based on whether or not a certain scope has been granted by the user, you might need to make a request for an additional scope in order to support a particular interaction.
2. Request additional scopes
If you need to request additional scopes, call
addScopes:presentingViewController:completion or
addScopes:presentingWindow:completion to ask the user to grant your app
additional access.
For example, to request read-only access to a user's Drive files:
Swift
letadditionalScopes=["https://www.googleapis.com/auth/drive.readonly"]
guardletcurrentUser=GIDSignIn.sharedInstance.currentUserelse{
return;/* Not signed in. */
}
currentUser.addScopes(additionalScopes,presenting:self){signInResult,errorin
guarderror==nilelse{return}
guardletsignInResult=signInResultelse{return}
// Check if the user granted access to the scopes you requested.
}
Objective-C
NSArray*additionalScopes=@[@"https://www.googleapis.com/auth/drive.readonly"];
GIDGoogleUser*currentUser=GIDSignIn.sharedInstance.currentUser;
[currentUseraddScopes:additionalScopes
presentingViewController:self
completion:^(GIDSignInResult*_NullablesignInResult,
NSError*_Nullableerror){
if(error){return;}
if(signInResult==nil){return;}
// Check if the user granted access to the scopes you requested.
}];
3. Make an API call with fresh tokens
To ensure that your Google API calls always have unexpired access tokens
attached, wrap the calls in a refreshTokensIfNeededWithCompletion: block:
Swift
currentUser.refreshTokensIfNeeded{user,errorin
guarderror==nilelse{return}
guardletuser=userelse{return}
// Get the access token to attach it to a REST or gRPC request.
letaccessToken=user.accessToken.tokenString
// Or, get an object that conforms to GTMFetcherAuthorizationProtocol for
// use with GTMAppAuth and the Google APIs client library.
letauthorizer=user.fetcherAuthorizer()
}
Objective-C
[currentUserrefreshTokensIfNeededWithCompletion:^(
GIDGoogleUser*_Nullableuser,
NSError*_Nullableerror){
if(error){return;}
if(user==nil){return;}
// Get the access token to attach it to a REST or gRPC request.
NSString*accessToken=user.accessToken.tokenString;
// Or, get an object that conforms to GTMFetcherAuthorizationProtocol for
// use with GTMAppAuth and the Google APIs client library.
id<GTMFetcherAuthorizationProtocol>authorizer=[userfetcherAuthorizer];
}];
Use the access token to call the API, by either including the access token in
the header of a REST or gRPC request (Authorization: Bearer ACCESS_TOKEN),
or by using the fetcher authorizer with the
Google APIs Client Library.