Override default functionality for Parse Server express routes

New Feature / Enhancement Checklist

• [ x ] I am not disclosing a vulnerability.
• [ x ] I am not just asking a question.
• [ x ] I have searched through existing issues.

Current Limitation

Currently, it's not possible to modify the default routing behaviour for Parse Server. For example, we want to be able to customise our login to be handled outside of Parse's own handler and then respond to the client seamlessly as if they are interacting with Parse. At present, there isn't a clean way to achieve this.

Feature / Enhancement Description

An interface to override specific routes with custom functionality.

Example Use Case

We want to override Parse's default login functionality and implement my own that reaches out to a third party API. Once the response is returned from said API, it would pass down the correct response to satisfy the client without any code changes required client-side.

Alternatives / Workarounds

Iterating over mounted routes and overriding the express handler function.

3rd Party References

No

Start by reviewing how Parse Server mounts its Express routes and how the current handlers are selected. Define an interface for overriding specific routes, using the login example as the target behavior. Done should allow a custom login implementation to return a response that Parse clients can consume without client-side changes.