Create simple Rest API

I have a php based management portal that i wish to create RestAPI for 3rd party access.
The authentication should be simply username & password and passed with each call (so not token based)

Below are the routes:

- (post) create a new client for the seller (seller login is required)
Output: user_name, password
- (post) assign the new user a package
- (put) extend sellers client package
- (delete) remove seller's client
- Get seller's client balance & expiration date

I will share relevant current PHP files for each methoud.