X509_verify_cert - discover and verify X509 certificte chain
int X509_verify_cert(X509_STORE_CTX *ctx);
If a complete chain can be built and validated this function returns 1, otherwise it return zero, in exceptional circumstances it can also return a negative code.
If the function fails additional error information can be obtained by
examining ctx using, for example
Applications rarely call this function directly but it is used by OpenSSL internally for certificate validation, in both the S/MIME and SSL/TLS code.
The negative return value from
This function uses the header x509.h as opposed to most chain verification functiosn which use x509_vfy.h.