Default DismissButtonStyle when using SFSafariViewController iOS 11+

[andrewfoghel]

Issue: #283

Issue: https://community.auth0.com/t/done-button-in-webview/23718/4

Description

This PR handles setting the SFSafariViewController.dismissButtonStyle to .cancel when using the useLegacyAuthentication(withStyle:) method. Above are 2 places where people have asked for this feature, and I'm sure they aren't the only ones who need this support.

Testing

We've added a spec to ensure that this gets set properly when using useLegacyAuthentication(withStyle:), however; the test will only run on iOS 11.0 and up. If there are any ideas for testing this please let me know.

Screenshots/GIFs

[andrewfoghel]

Closing as there are failures, going to investigate.

[cocojoe]

@andrewfoghel Thanks for the PR and screenshot. What is the use case? I noticed the other issues but they also give no reason as to why it's important.

Looking at the above I feel that the current default Done is not really the optimal value and the value should instead align with Apple's recommended WebAuth flow in iOS 11+. This uses Cancel which makes sense from an end user perspective as you are cancelling Web Auth.

So I think it should default to Cancel to match Apple's behaviour. However, not sure on it being configurable. Does this align with why you wanted to change it?

[andrewfoghel]

@cocojoe Thanks for the response here! This use case is more so for people using the useLegacyAuthentication() helper. It gives people access to customize that button when using an SFSafariViewController. I believe that when using ASWebAuthenticationSession it is always Cancel and that you can't change that value. However, for SFSafariViewController it gets defaulted to Done so allowing them to change it to Close or Cancel gives them the opportunity to maintain more consistency throughout their application. Thoughts?

[andrewfoghel]

We will not be using the useLegacyAuthentication() helper anymore, so we personally don't need this as a part of the SDK. However, I don't want to take from the community that uses that method, thus; I'll leave this open. Feel free to close this if this functionality is deemed as unnecessary or overkill. Thanks for the careful consideration with this!

On a separate note, if you all decide that you want this feature in I will maintain this PR.

[cocojoe]

@andrewfoghel I feel we can address the root cause here changing the default of the Library to specify Cancel which aligns with Apple's current default messaging in ASWebAuthentictionSession.

This should address the concern without having to expose additional methods to allow this to be changed by the developer.

[andrewfoghel]

@cocojoe I was thinking it would be nice to give the developer the option to choose whichever option they want; however, I'm not opposed to simply defaulting the button to say Cancel to match ASWebAuthenticationSession. Those changes should be reflected in the last few commits, let me know what you think!

[cocojoe]

@andrewfoghel Thanks for changing, I was on vacation, hence the delay in response :) Looks good 👍

[andrewfoghel]

@cocojoe thanks for the approval here! I'm going to delete the branch for prosperity, til next time! (: