Harden SOAP API Access Control

I need a security specialist to lock down my publicly facing SOAP API. Right now it is shielded only by Basic Authentication, and I am concerned this is not enough to prevent unauthorized access. Your... (Budget: ₹12500 - ₹37500 INR, Jobs: Computer Security, Incident Response, Internet Security, OAuth, Penetration Testing, PHP, Security Auditing, Web Security)