How to use my own root certificate in iOS Secure Transport API?

I'm trying to use Apple's Secure Transport API on top of an established transport layer, with my own root certificate. I have my root certificate as a SecCertificateRef, but I can't figure out how to make it trusted.

I've examined the following functions, each of which seems tantalizingly close to what I need:

• SSLAddDistinguishedName() is unimplemented;
• SSLSetTrustedRoots() is deprecated;
• SSLSetCertificateAuthorities() is for client authentication only.

If I could override the SecTrustRef within the SecContextRef, then SecTrustSetAnchorCertificates() would do the job. Unfortunately, this avenue only led me to SSLGetPeerSecTrust() which seems to be an Apple-private API.