X509_set0_signature API is missing

https://www.openssl.org/docs/man1.1.1/man3/X509_get0_signature.html

This documentation states:

These functions provide lower level access to signatures in certificates where an application wishes to analyse or generate a signature in a form where X509_sign() et al is not appropriate (for example a non standard or unsupported format).

The implication here is that these functions intentionally allow modifying the signature of an x509 structure. These shouldn't be const. Otherwise, there should be a X509_set_signature().