Support for client certificate authentication during OAuth 2.0

[NicholasMata]

changelog(Improvements): Added support for Client Certificate Authentication during OAuth 2 fetch token

Adds support for Client Certificate Authentication during the OAuth 2 browser popup. This form for authentication is well known and supported by all major browsers (Safari, Chrome, Edge, etc)

This fix will automatically select the first certificate if there is only a single certificate. If there are multiple valid certificates it will prompt the user to select one.

Closes #4960 and possibly #1250

[filfreire]

Hi @NicholasMata thanks for contributing this PR and reporting the original issue.

It might take a while for us to look deeply into this PR.

Any chance you can share tips on how to test this PR or resources (e.g. docs, an existing repo, docker container, ...) that would help us experiment with it faster?

[NicholasMata]

As far as testing with authentication that returns a token I could set something up but might take a while. I have tested against my own organization's authentication server which I can't give access too.

But to test the functionality of selecting a certificate you can do the following.

Create a new HTTP Request in Insomnia. Then set Auth to OAuth 2.0. Then select Implicit for Grant Type and https://server.cryptomix.com/secure/ for Authorization Url. Then you can go a head and Fetch Tokens. With this PR you will see a popup window to select a certificate when you have more than one valid certificate available. Then you will see the site show the certificate information for the one that you selected. It won't return a token as I mentioned before I can setup an authentication server if needed.

https://server.cryptomix.com/secure/ will require you to select a certificate and it will display all the information about the certificate you selected. You can test it in any browser as well.

If you need to create a certificate you can do the following on macOS. Unfortunately I am not sure the steps for Windows off the top of my head.

1. Open up Keychain
2. Select "Keychain" at the top left of the screen.
3. Hover over "Certificate Assistant"
4. Select "Create a Certificate..."
5. Name it whatever you want
6. Set "Identity Type" to "Self Signed Root"
7. Set "Certificate Type" to "SSL Client"
8. Then you can "Create" it.

[wongstein]

Ah, I can confirm that the PR does what it purports. Following the instructions given, here is what latest 2022.5.1 Insomnia gives (no option to select certificate)

And here's the PR's options to select a certificate

[filfreire]

Tested locally on MacOS, LGTM

On Windows I've tried and seems I can't get the select-client-certificate to get triggered for now.

[filfreire]

Also managed to test it properly on windows, seems to work fine