🚀 Feature: PKCE for OAuth2 providers

[tanay1337]

🔖 Feature description

It doesn't seem like the OAuth2 providers use PKCE with the authorization code flow from a cursory view. The PKCE implementation would be helpful to avoid auth code injection attacks.

🎤 Pitch

This should probably be abstracted away in appwrite/src/Appwrite/Auth/OAuth2.php so that contributors building new providers don't have to interact with the PKCE code. Here's an example of PKCE implementation in PHP.

👀 Have you spent some time to check if this issue has been raised before?

• I checked and didn't find similar issue

🏢 Have you read the Code of Conduct?

• I have read the Code of Conduct

[stnguyen90]

PKCE is used for client side. However, the auth code flow Appwrite does is server side so it shouldn't be a problem.