Need to check for standard API to create an interface from a 3rd party system to repository contract

We are looking for any standard API available within procurement contracts that would enable an interface to be created from a 3rd party tool to repository contracts. Please note that we primarily use repository contracts to store standalone contracts with no integration with procurement with user defined types. We also attach contract documents to these records and update risks and party contracts. We are looking for an interface that would create repository contracts from a 3rd party tool. Below are the fields that we need to be populated in repository contracts from the 3rd party tool via interface Amount Authoring Party