Need Develop Custom API Connect to remote DataBase

I currently have a fully developed script that works properly. The script is divided into two parts, one runs on the server and the other on the client, the script on the client calls the server to use these files and process payments. The problem is that currently the server uses the client database directly and whitelisted in cpanel to allow connection and it only works with 1 client. It seeks to develop an API that connects to the remote database of clients through the web server and PHP without opening ports or allowing direct access to the server from external sources or using whitelist in the case of Cpanel, which allows multiple clients connect and consume the server API. The client needs to call the server through the custom API and send the corresponding information, to use the files that are on the server and process the payments. IMPORTANT: The script will be delivered encrypted so the freelancer must carry out the development of the project between the two points that are available without encryption (Server -> [login to view URL] / [login to view URL] // Client -> [login to view URL] / Client UI calls [login to view URL]) Requirements: 1. Make PHP API connect to remote client database through web server and PHP without opening ports or without allowing direct access to database server from external sources, API must allow to connect to several clients to the server automatically, the APi must obtain the information from the client's database to generate and return the result. (Sebe must implement something like a MYSQLTUNNEL to connect client and server or an API with SOAP between client and server) 2. After developing the custom API, an authentication system must be implemented: The API must be used exclusively by authenticated clients, the authentication will be done with the domain / subdomain name and the client's license as the authentication method. For this point, a MYSQL table is used on a server where there is a list with linked domains and licenses that is constantly updated. 3. It is very important that security measures are implemented (the information between client and server must be encrypted using some option such as JWT, OpenSSL, AES) 4. The API carried out must generate a log of the users who use / call it with the data: Date, IP, domain / subdomain This log can be consulted in a simple page of the server that is shown as a table with the following columns: Date, IP, Domain, Action and it will be cleaned automatically every 60 days without using CRON, you can use a timestamp and put a button to delete them manually. 5. You must make a simple page that shows a blacklist as a table in PHP on the server and that allows adding to the blacklist the domains / subdomains or IP's that cannot use the API (, , any .), the blacklist will be handled in a MYSQL table on the server indicated above, the table in the database must be called api_blacklist_service. The selected Freelancer will only have access to the FTP, Database Access data, the freelancer must carry out the development on the client and server delivered where they can perform the corresponding tests and development.