Add something similar to onReceivedHttpAuthRequest from Android Version to iOS Version

# Feature Request

## Motivation Behind Feature
We want to perform basic auth.

## Feature Description
In the Android Version of this plugin it is possible to "inject" some basic auth. We want to do this in the ios Version aswell.

## Alternatives or Workarounds
We extendes the method onReceivedHttpAuthRequest in android like so:

```
if (UserName != null && Password!= null) {
handler.proceed(UserName, Password);
return;
}
```

Username and password will be fetched out of a parameter from the url.

Start by comparing the Android implementation of onReceivedHttpAuthRequest with the iOS version of this plugin and identify the corresponding authentication entry point. Confirm how the requested username and password are supplied, then verify that iOS can provide equivalent basic-auth handling and that the feature works for an authenticated URL.

Written by the indexing model from the issue text.