The instructions you linked to require that the mobile app is installed, and the authentication happens by interacting with the native code:
Currently, only the original login method is allowed for WeChat login via mobile application, therefore users need to install the WeChat client.
With the current Auth0 product offering, the Custom Social Connections extension could be used to create an OAuth2 connection to WeChat (although we would have to tinker to rename the parameters since WeChat doesn’t use the standard OAuth2 parameter names). But that would only work on non-mobile devices, since this uses HTTP requests (it can’t interact with native apps). I can help you with this, but since it would take time I want to make sure it would be helpful to have WeChat authentication support only on desktop browsers, which I’m guessing won’t be enough.
Support for authenticating directly with a native app (basically the option to exchange a WeChat access token for an Auth0 access token) so that WeChat authentication can be used on any device would require modifications to the product (i.e. this is a feature request), it’s not possible at this moment. So, for this, Auth0: Secure access for everyone. But not just anyone. is the best option to reach out to the Product team.