def get_subj_alt_name(peer_cert: X509) -> list[tuple[str, str]]:
    """
    Given an PyOpenSSL certificate, provides all the subject alternative names.
    """
    cert = peer_cert.to_cryptography()

    # We want to find the SAN extension. Ask Cryptography to locate it (it's
    # faster than looping in Python)
    try:
        ext = cert.extensions.get_extension_for_class(x509.SubjectAlternativeName).value
    except x509.ExtensionNotFound:
        # No such extension, return the empty list.
        return []
    except (
        x509.DuplicateExtension,
        UnsupportedExtension,
        x509.UnsupportedGeneralNameType,
        UnicodeError,
    ) as e:
        # A problem has been found with the quality of the certificate. Assume
        # no SAN field is present.
        log.warning(
            "A problem was encountered with the certificate that prevented "
            "urllib3 from finding the SubjectAlternativeName field. This can "
            "affect certificate validation. The error was %s",
            e,
        )
        return []

    # We want to return dNSName and iPAddress fields. We need to cast the IPs
    # back to strings because the match_hostname function wants them as
    # strings.
    # Sadly the DNS names need to be idna encoded and then, on Python 3, UTF-8
    # decoded. This is pretty frustrating, but that's what the standard library
    # does with certificates, and so we need to attempt to do the same.
    # We also want to skip over names which cannot be idna encoded.
    names = [
        ("DNS", name)
        for name in map(_dnsname_to_stdlib, ext.get_values_for_type(x509.DNSName))
        if name is not None
    ]
    names.extend(
        ("IP Address", str(name)) for name in ext.get_values_for_type(x509.IPAddress)
    )

    return names

    Given an PyOpenSSL certificate, provides all the subject alternative names.
    
src/urllib3/contrib/pyopenssl.py