OpenSSL::X509::StoreContext#purpose=

static VALUE
ossl_x509stctx_set_purpose(VALUE self, VALUE purpose)
{
    X509_STORE_CTX *store;
    int p = NUM2INT(purpose);

    GetX509StCtx(self, store);
    X509_STORE_CTX_set_purpose(store, p);

    return purpose;
}