Google Classroom API integration with swift - swift

Question

I want to link my iOS app with Google Classroom on swift. My current goal is to be able to get a list of all the courses I am enrolled in.
Here is the code I am currently using
func googleClassroomList() {
//let sharedInstance = GIDSignIn.sharedInstance()
//let handler = sharedInstance
googleClassroomService.apiKey = "AIzaSyBOGamjhRuu45T2jT7Qa3LmtntSwgIxeqo"
let query = GTLRClassroomQuery_CoursesList.query()
query.pageSize = 1000
let classQuery = googleClassroomService.executeQuery(query, completionHandler: { ticket , fileList, error in
if error != nil {
let message = "Error: \(error?.localizedDescription ?? "")"
print(message)
} else {
if let list = fileList as? GTLRClassroomQuery_CoursesList {
self.fileList = list
print("List: \(list)")
}
else {
print("Error: response is not a file list")
}
}
}
)
}
Here is the error message:
Error: Request is missing required authentication credential. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.
I don't understand where I attach the OAuth access token, I tried putting it under apiKey but I don't really understand what I am supposed to do. For reference, I am using this auth scope. "https://www.googleapis.com/auth/classroom.courses"

Answer 1

First you have to sign-in using Google, and Google will manage the OAuth 2.0 token for you.
Here you have the instructions:
https://developers.google.com/identity/sign-in/ios/sign-in?ver=swift
Also make sure to set the service.authorizer property when you are actually signed in:
func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!,
withError error: Error!) {
guard let user = user else {
return
}
let appDelegate = UIApplication.shared.delegate as! AppDelegate
appDelegate.setLoggedOut(loggedOut: false)
self.myClassroom.service.authorizer = user.authentication.fetcherAuthorizer()
self.showClassroomClasses()
}