[BE] 10-10CG - Improvements: Implement OAuth 2.0 for MuleSoftClient behind flipper toggle

[coope93]

As a first step for implementing OAuth 2.0 Authentication for the 10-10CG form, we need to update the existing MuleSoftClient to use the new authentication flow.

• This will need to be behind a flipper toggle so we can turn it on for validation in lower environments.
• More than likely this will follow a client credential grant flow (confirmed this is the case) as it is service to service authentication.
• Helpful info for OAuth 2.0 Client Credential flow with Okta is here
• SI (DEV/QA) or DTC-I team (Stage/Prod) will create the application through AnyPoint Exchange for the API which is requested access by the consumer (va.gov)
• DTC-I team will provide us the auth server URL, Client Id, and Client Secret in an encrypted email. (These will need added to AWS Parameter Store with a platform support ticket)

[hdjustice]

closed as duplicate. Using #86425