How to generate with openSSL a key pair + CSR with a custom field name and value?

Question

I need to generate a certificate requests, with a specific field "Email". I've created a configuration file to generate my request, but I can't find a way to have this "non-standard" field in my CSR.

Here is my command line openssl req -new -newkey rsa:2048 -noenc -pubkey -config config_file.cnf -keyout my_key.key -out my_csr.csr

My config file content :

 [ req ]
 default_bits           = 2048
 prompt                 = no
 distinguished_name     = req_distinguished_name

 [ req_distinguished_name ]
 CN=XXXXXXX
 OU=XXXXXXX
 O=XXXXXXX
 L=XXXXXXX
 ST=XXXXXXX
 C=XXXXXXX
 subjectKeyIdentifier=hash
 subjectAltName=XXXXXXX
 keyUsage=digitalSignature
 extendedKeyUsage=clientAuth
 [email protected]

With this configuration, I get the following error:

x509 certificate routines:X509_NAME_ENTRY_create_by_txt:invalid field name:../crypto/x509/x509name.c:249:name=Email

I know that there is an "emailAddress" field but it's not what I am asked.

I've tried to set the field in a "req_extensions", but without success.

I've also tried using OIDs (though I'm not sure if that's the right thing to do), but when look at the content of the CSR file (with openssl req -text -in my_csr.csr), I see the numbers associated with the OID and not the field name.