File access levels
When adding the Storage category, you configure the level of access users have to your S3 bucket. You can configure separate rules for authenticated vs. guest users. When using the Storage category to upload files, you can also specify an access level for each individual file: guest, protected, or private.
- Guest Accessible by all users of your application
- Protected Readable by all users, but only writable by the creating user
- Private Readable and writable only by the creating user
Guest access does not mean that your files are totally public. A "guest" is a user of your application who has not yet signed in. To enable access at this level, you will still be required to configured Authentication in your app. The user must be able to assume an unauthenticated role from your Cognito Identity Pool.
For protected and private access, the [IDENTITY_ID] below corresponds to the unique ID of the user. Once the user has signed in, the [IDENTITY_ID] can be retrieved from the session by accessing the identity id. See Accessing credentials to retrieve the identity id, and use this as the unique ID of the authenticated user.
Protected access
After the user has signed in, create an options object specifying the protected access level to allow other users to read the object:
func uploadData(key: String, data: Data) { let options = StorageUploadDataRequest.Options(accessLevel: .protected) Amplify.Storage.uploadData(key: key, data: data, options: options) { progress in print("Progress: \(progress)") } resultListener: { event in switch event { case .success(let data): print("Completed: \(data)") case .failure(let storageError): print("Failed: \(storageError.errorDescription). \(storageError.recoverySuggestion)") } }}var progressSink: AnyCancellable?var resultSink: AnyCancellable?
func uploadData(key: String, data: Data) { let options = StorageUploadDataRequest.Options(accessLevel: .protected) let storageOperation = Amplify.Storage.uploadData(key: key, data: data, options: options) progressSink = storageOperation.progressPublisher.sink { progress in print("Progress: \(progress)") } resultSink = storageOperation.resultPublisher.sink { if case let .failure(storageError) = $0 { print("Failed: \(storageError.errorDescription). \(storageError.recoverySuggestion)") } } receiveValue: { data in print("Completed: \(data)") }}This will upload with the prefix /protected/[IDENTITY_ID]/ followed by the key.
For other users to read the file, you must specify the access level as protected and the identity ID of the user who uploaded it in the options.
func downloadData(key: String, identityId: String) { let options = StorageDownloadDataRequest.Options(accessLevel: .protected, targetIdentityId: identityId) Amplify.Storage.downloadData( key: key, options: options, progressListener: { progress in print("Progress: \(progress)") }, resultListener: { (event) in switch event { case let .success(data): print("Completed: \(data)") case let .failure(storageError): print("Failed: \(storageError.errorDescription). \(storageError.recoverySuggestion)") } })}var progressSink: AnyCancellable?var resultSink: AnyCancellable? func downloadData(key: String, identityId: String) { let options = StorageDownloadDataRequest.Options(accessLevel: .protected, targetIdentityId: identityId) let storageOperation = Amplify.Storage.downloadData(key: key, options: options) progressSink = storageOperation.progressPublisher.sink { progress in print("Progress: \(progress)") } resultSink = storageOperation.resultPublisher.sink { if case let .failure(storageError) = $0 { print("Failed: \(storageError.errorDescription). \(storageError.recoverySuggestion)") } } receiveValue: { data in print("Completed: \(data)") }}Private Access
Create an options object specifying the private access level to only allow an object to be accessed by the creating user
let options = StorageUploadDataRequest.Options(accessLevel: .private)This will upload with the prefix /private/[IDENTITY_ID]/, followed by the key.
For the user to read the file, specify the same access level (private) and key you used to upload:
let options = StorageDownloadDataRequest.Options(accessLevel: .private)Customization
Customize Object Key Path
You can customize your key path by defining a prefix resolver:
import Amplifyimport AmplifyPlugins
// Define your own prefix resolver, that conforms to `AWSS3StoragePluginPrefixResolver`struct MyDeveloperDefinedPrefixResolver: AWSS3PluginPrefixResolver {
// This function is called on every Storage API to modify the prefix of the request. func resolvePrefix( for accessLevel: StorageAccessLevel, targetIdentityId: String?, completion: @escaping (Result<String, StorageError>) -> Void ) { // Use "myPublicPrefix" for guest access levels if accessLevel == .guest { completion(.success("myPublicPrefix/")) return }
// Use "myProtectedPrefix/{targetIdentityId}" and "myPrivatePrefix/{targetIdentityId}" respectively // `targetIdentityId` is the value passed into the Storage request object, if let identityId = targetIdentityId { if accessLevel == .protected { completion(.success("myProtectedPrefix/" + identityId + "/")) } else if accessLevel == .private { completion(.success("myPrivatePrefix/" + identityId + "/")) } return }
// Use "myProtectedPrefix/{identityId}" and "myPrivatePrefix/{identityId}" respectively // `identityId` is the identity id of the current user getIdentityId { result in switch result { case .failure(let error): completion(.failure(error)) case .success(let identityId): if accessLevel == .protected { completion(.success("myProtectedPrefix/" + identityId + "/")) } else if accessLevel == .private { completion(.success("myPrivatePrefix/" + identityId + "/")) } } } }
public func getIdentityId(completion: @escaping (Result<String, StorageError>) -> Void) { Amplify.Auth.fetchAuthSession { result in do { let session = try result.get() if let identityProvider = session as? AuthCognitoIdentityProvider { let identityId = try identityProvider.getIdentityId().get() completion(.success(identityId)) } } catch { completion(.failure(StorageError.authError("Failed to retrieve auth session", "", error))) } } }}Then configure the storage plugin with the resolver.
let storagePlugin = AWSS3StoragePlugin(configuration: .prefixResolver(MyDeveloperDefinedPrefixResolver()))Amplify.add(storagePlugin)Add the IAM policy that corresponds with the prefixes defined above to enable read, write and delete operation for all the objects under path myPublicPrefix/:
"Statement": [ { "Effect": "Allow", "Action": [ "s3:GetObject", "s3:PutObject", "s3:DeleteObject" ], "Resource": [ "arn:aws:s3:::your-s3-bucket/myPublicPrefix/*", ] }]If you want to have custom private path prefix like myPrivatePrefix/, you need to add it into your IAM policy:
"Statement": [ { "Effect": "Allow", "Action": [ "s3:GetObject", "s3:PutObject", "s3:DeleteObject" ], "Resource": [ "arn:aws:s3:::your-s3-bucket/myPrivatePrefix/${cognito-identity.amazonaws.com:sub}/*" ] }]This ensures only the authenticated users has the access to the objects under the path.
Passthrough PrefixResolver
If you would like no prefix resolution logic, such as performing S3 requests at the root of the bucket, create a prefix resolver that returns an empty string:
public func resolvePrefix( for accessLevel: StorageAccessLevel, targetIdentityId: String?) -> Result<String, StorageError> { return .success("")}Client validation
You can also perform validation based on the access controls you have defined. For example, if you have defined Guests with no access then you can fail the request early by checking if the user is not signed in:
struct MyDeveloperDefinedPrefixResolver: AWSS3PluginPrefixResolver { public func resolvePrefix( for accessLevel: StorageAccessLevel, targetIdentityId: String?, completion: @escaping (Result<String, StorageError>) -> Void ) { guard Amplify.Auth.getCurrentUser() != nil else { completion(.failure(.authError("User is not signed in", "", nil))) return }
// Continue to resolve the prefix for the request // ... }}