static int x509_info_subject_alt_name( char **buf, size_t *size,
                                       const mbedtls_x509_sequence *subject_alt_name )
{
    size_t i;
    size_t n = *size;
    char *p = *buf;
    const mbedtls_x509_sequence *cur = subject_alt_name;
    const char *sep = "";
    size_t sep_len = 0;

    while( cur != NULL )
    {
        if( cur->buf.len + sep_len >= n )
        {
            *p = '\0';
            return( MBEDTLS_ERR_X509_BUFFER_TOO_SMALL );
        }

        n -= cur->buf.len + sep_len;
        for( i = 0; i < sep_len; i++ )
            *p++ = sep[i];
        for( i = 0; i < cur->buf.len; i++ )
            *p++ = cur->buf.p[i];

        sep = ", ";
        sep_len = 2;

        cur = cur->next;
    }

    *p = '\0';

    *size = n;
    *buf = p;

    return( 0 );
}

When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.