Custom workflow for non-standard OAuth2

**Is your feature request related to a problem? Please describe.**
For [DingTalk](https://open.dingtalk.com/document/orgapp/obtain-identity-credentials#title-yr2-ahi-1er), it does not follow the standard OAuth2 protocol.
Specifically, the parameters used to get `access_token` is send in *camelCase* rather than *snake_case*. So currently, I cannot set it up without modifying the source code. Or maybe there exist other solutions?

**Describe the solution you'd like**
We could add concepts like `property / field mapping` or `request interceptor` for the non-standard OAuth2 protocol implementations.

**Describe alternatives you've considered**
[Ory Kratos](https://www.ory.sh/docs/kratos/social-signin/dingtalk) has something similar.

**Additional context**
No

The issue identifies DingTalk's non-standard OAuth2 token parameters and suggests property mapping or a request interceptor, but it names no files, tests, or entry points. Start by locating the OAuth2 client implementation and existing provider configuration; done would require an agreed, tested way to support this flow without source modifications.

Written by the indexing model from the issue text.