How to use an AWS federated token with AWS iOS SDK 2.0

I've checked the AWS docs, and everything there points to Cognito, can't find how to just use an AccessKeyId and a SecretAccessKey.

All user management and authentication takes place on the server. There's a long access policy that the server determines based on specific user permissions, and then the server generates a temporary FederationToken with that policy and passes that to the iOS app to use.

Does anyone have a code sample of how to use that passed Federated user in iOS to upload an item to s3?

Thanks