feat(core): add core functions for external authentication

[hrithikesh026]

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

Added core functions to take care of pre_authentication, authentication and post_authentication operations.

defined 3 functions perform_pre_authentication, perform_authentication and perform_post_authentication and other dependencies for these functions.

These 3 functions will act as the entry point to the authentication module.

These functions are not being called currently from any flow. That will be done is a separate PR.

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables

Motivation and Context

To achieve external authentication.

How did you test it?

Compiler guided and Sanity testing to make sure it's backward compatible

This PR cannot be tested until core changes are done.

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed the submitted code
• I added unit tests for my changes where possible
• I added a CHANGELOG entry if applicable

[Narayanbhat166]

Please address the refactorings, can be taken up in a separate PR.

[prajjwalkumar17]

LGTM! eventhough no Routing changes found in this PR.