Function mbedtls_x509write_csr_set_extension 

pub unsafe extern "C" fn mbedtls_x509write_csr_set_extension(
    ctx: *mut mbedtls_x509write_csr,
    oid: *const c_char,
    oid_len: usize,
    critical: c_int,
    val: *const c_uchar,
    val_len: usize,
) -> c_int

\brief Generic function to add to or replace an extension in the CSR

\param ctx CSR context to use \param oid OID of the extension \param oid_len length of the OID \param critical Set to 1 to mark the extension as critical, 0 otherwise. \param val value of the extension OCTET STRING \param val_len length of the value data

\return 0 if successful, or a MBEDTLS_ERR_X509_ALLOC_FAILED