How to change the basic Authorization header in the policies?

[subhajit2022]

I am new to APIGEE and have the following use case -

• request comes to APIGEE with basic Authorization header . The value is base64 encoded. Client also passes a custom auth header which is required by the backend.
• after APIGEE verify the caller I need to change the basic Authorization header to a different value which client passes through custom auth header.
• Then remove the custom auth header and call to backend 

please help me on this .