Pass new user agent prefix for Amplify calls

[palpatim]

Currently the API category uses a user agent specified in a constants file (see #75). We need to update this:

• Use exact same user agent pattern as we do in the iOS SDK (https://github.com/aws-amplify/aws-sdk-ios/blob/afcce622023a8885ebfc676f6c83e6db8e7d7915/AWSCore/Service/AWSService.m#L158), except change the prefix to "amplify-iOS" instead of "aws-sdk-iOS": amplify-iOS/<version> <systemName/<systemVersion> <locale>

• Use the user agent for all calls into AWS services, not just API calls. This means we'll have to plumb the user agent string to be overwritable by Amplify calls, but not universally overwritable. We'll need to discuss the best way to do this.

[lawmicha]

@royjit 's previous work #166 .

• PR is closed and not merged (was pending some decision that i can't remember what it was right now.
• Implementation uses a subclass of AWSServiceConfiguration to override the default useragent

[wooj2]

I did a deep dive last week of the user-agents we have been sending out.

Currently in Production:

AWS SDK iOS

Constructed as part of AWSCore, the user agent looks like the following:

    "aws-sdk-iOS/<version> iOS/<iosVersion> <locale>"

(Note that there can be some variations if you look at line 179 of AWSService.m)

Amplify Storage/Predictions & other categories using the AWS SDK iOS (BUT NOT Amplify API/DataStore)

Since Jithin’s PR has not been pushed to mainline yet, the user agent should be using the same user agent as the AWS iOS SDK, so therefore, it should be:

    "aws-sdk-iOS/<version> iOS/<iosVersion> <locale>"

Amplify API (and Amplify DataStore):

When using IAM or userPools, the user agent is:

    "amplify-ios/0.9.0 Amplify"

When using an APIkey, we are not setting the user agent (this is a bug, and we need to fix this)

    Currently a bug, and will need to get fixed

AppSync

Based on this link: https://github.com/awslabs/aws-mobile-appsync-sdk-ios/blob/master/AWSAppSyncClient/AWSAppSyncHTTPNetworkTransport.swift#L114
We seem to be sending out a user agent of:

    “aws-sdk-ios/3.0.0 AppSyncClient"

In the short term (prior to P31016485 getting resolved -- e.g. backend parsing being completed):

We recommend two immediate changes.

1. Change Amplify API user agent from:

“amplify-ios/0.9.0 Amplify”

To:

"aws-sdk-iOS/2.12.2 iOS/<iosVersion> <locale>"

We believe that by making this change, the metrics team will be able to provide us some basic usage metrics (despite not being able to differentiate between actual SDK usage vs amplify usage)
2. Fix the bug in Amplify API to set the user-agent when using an API key.

Longer term (but hopefully not too long)

Sit down with the metrics team to agree on a format for the user agent we send from the amplify clients to the backend services so that we can clearly attribute calls from amplify vs calls from AWS SDK iOS.
Make appropriate changes & test

[wooj2]

Sync'ed with Mohit from the product side, we have decided that

1. We will not be doing a "short term fix"
2. the desired user agent on iOS will be in the following format:

amplify-iOS/<version> <systemName>/<systemVersion> <locale>

[wooj2]

PR here: #273

[wooj2]

Verification of building amplify into a sample app and making a GraphQL call via data store.

[wooj2]

Verification of building storage api into a sample app and making a storage call

One thing i did notice however is that when we authenticate via codigo, we are continuning to use the aws-sdk-ios user agent from that call, but i suppose that is expected.

[wooj2]

Three more items we should verify w/ charles proxy prior to closing this issue:

• API-REST calls
• Predictions
• Pinpoint

[wooj2]

Verification of predictions calls:

[wooj2]

Verified with api w/ apikey... didn't verify other mechanisms, but based on how the code is structured w/ interceptors, we should be good to go on the API category.

[wooj2]

Verified pinpoint:

manually verified each of the categories, lgtm!