X509_STORE_CTX_set_purpose
X509_STORE_CTX_set_purpose(ctx, X509_PURPOSE_OCSP_HELPER);
X509_STORE_CTX_set_purpose(ctx, X509_PURPOSE_SMIME_SIGN);
X509_STORE_CTX_set_purpose(cert_ctx, X509_PURPOSE_TIMESTAMP_SIGN);
int X509_STORE_CTX_set_purpose(X509_STORE_CTX *ctx, int purpose);
if (!TEST_true(X509_STORE_CTX_set_purpose(ctx, purpose)))