How do I use an iOS app's bundle identifier to 'authorize' upload to Google Cloud Storage? - ios

Question

Our service is using Google App Engine as our backend, and we're now implementing an upload-function for images etc.
Using the answers from several different questions here on stack, I have made it working, but not completely as I want. We are not using the built-in OAuth etc, and for now we want the storage to be public, but not entirely public. We would like to limit it to users of our own app (I.E no authentication). In the Cloud-console we can create an API-key for iOS. When doing this, we copy the API-key to the app, and pass it along with every upload-request. This is currently working, when the bucket-permission is set to allUsers - WRITE
However, inside the API-key, we can supply our app's own Bundle Identifier, so that, supposedly, only requests from our app is allowed. (App Store ID/URL is also permitted, apparently).
Adding this bundle-id does nothing as long as the bucket has the permission allUsers - WRITE. If I change the bundle-id to not match the actual bundle-id, it still works. So which permission should it use for the bucket to make the bundle-id in the API-key apply? And what should be sent along in the upload-code on iOS (acl?)?.
If I remove the allUsers-permission, and use something else, I get this error when trying to upload:
{message:"There is a per-IP or per-Referer restriction configured
on your API key and the request does not match these
restrictions. Please use the Google Developers Console
to update your API key configuration if request from this
IP or referer should be allowed." data:[1] code:403}}
This is how I'm using it right now (though I have tried several different things, all picked up from different questions/answers):
GTLServiceStorage *serv = [[GTLServiceStorage alloc] init];
serv.additionalHTTPHeaders = [NSDictionary dictionaryWithObjectsAndKeys:
#"[my project id]", #"x-goog-project-id",
#"application/json-rpc", #"Content-Type",
#"application/json-rpc", #"Accept", nil];
serv.APIKey = #"[my iOS API key, gotten from console, (linked to bundle-id?)]";
serv.retryEnabled = YES;
GTLStorageBucket *bucket = [[GTLStorageBucket alloc] init];
bucket.name = #"[my bucket]";
GTLUploadParameters *params = [GTLUploadParameters uploadParametersWithFileHandle:fileHandle MIMEType:#"image/jpeg"];
GTLStorageObject *storageObject = [[GTLStorageObject alloc] init];
storageObject.name = #"testFile.jpg";
//I have no idea what I'm doing with the following stuff, but I've tried several things:
GTLStorageObjectAccessControl *objAccessControl
= [GTLStorageObjectAccessControl new];
//This is working
objAccessControl.entity = #"allUsers";
objAccessControl.email = #"[my app-id]#project.gserviceaccount.com";
objAccessControl.role = #"OWNER";
//If I try this instead, it is not working.
//objAccessControl.domain = #"[my app-id].apps.googleusercontent.com";
//objAccessControl.role = #"WRITER";
//Probably because it's bullshit, I have no idea what I'm doing.
storageObject.acl = #[objAccessControl];
[...] //Bucket and upload and stuff. It seems like it's the ACL-thing above that's not working..
It seems like I have to connect the permissions on the bucket to the iOS API Key somehow, but I don't know if it's even possible.
What I want: All users to be able to use the cloud, given that they are requesting it from my iOS app.

Answer 1

As this question never got an answer I'll add one here, based on the information currently in the post.
The reason you got the error 'There is a per-IP or per-Referer restriction..' when calling the GCS API with the iOS API Key is simply because the GCS API doesn't work with API Keys for private data, only Bearer Tokens (ie. using OAuth). There isn't anything you could have done to make the API Key work with the GCS API directly with private data. The reason it worked when you had 'allUsers - WRITE' set as the ACL is simply because that ACL allows public access.
To access the private data without user intervention requires a Service Account, however the Google APIs Objective-C Client only supports OAuth2 Client IDs. The rationale being that Service Accounts are intended for server-side authentication only. Using a Service Account in a client would involve distributing the private key along with the app, which could easily be compromised. For reference, here's a sample of how you might authorize the GCS service using OAuth:
NSString *keychainItemName = #"My App";
NSString *clientID = <your-client-id>;
NSString *clientSecret = <your-client-secret>;
// How to check for existing credentials in the keychain
GTMOAuth2Authentication *auth;
auth = [GTMOAuth2WindowController authForGoogleFromKeychainForName:kKeychainItemName
clientID:clientID
clientSecret:clientSecret];
...
// How to set up a window controller for sign-in
NSBundle *frameworkBundle = [NSBundle bundleForClass:[GTMOAuth2WindowController class]];
GTMOAuth2WindowController *windowController;
windowController = [GTMOAuth2WindowController controllerWithScope:kGTLAuthScopeStorageDevstorageFullControl
clientID:clientID
clientSecret:clientSecret
keychainItemName:kKeychainItemName
resourceBundle:frameworkBundle];
[windowController signInSheetModalForWindow:[self window]
completionHandler:^(GTMOAuth2Authentication *auth,
NSError *error) {
if (error == nil) {
self.storageService.authorizer = auth;
}
}];
...
// Initialize service with auth
GTLServiceStorage *serv = [[GTLServiceStorage alloc] init];
serv.authorizer = auth;
All of this was taken from the storage sample on the google-api-objectivec-client GitHub page, so you can refer to it for a complete example with context.
This still leaves the question of how to implement access to GCS from iOS without user authorization. The short answer to this is that the iOS Key can be used to restrict access to your own backend API hosted on Google Cloud Endpoints, and that backend application can authorize against GCS using a Service Account (usually the Application Default Service Account). The Cloud Storage Client Library Examples page has samples using the default credentials for different languages.
Further details on how to implement an Endpoints API for this purpose are probably getting outside of the scope of this question, but this should serve as a good starting point.