and is called by the CFSSL library, that has isCA = false as default (https://github.com/cloudflare/cfssl/blob/152152bec641f502651...)
Also it is verified that the CSR doesn't contain that field in Boulder: https://github.com/letsencrypt/boulder/blob/aa71088c440a63e1...
This test is called when you send the CA a CSR: https://github.com/letsencrypt/boulder/blob/08ac100788c7edaf...
I don't know for other CAs, but from that quick look of the code boulder doesn't seem to sign certificates that can sign other certificates.
and is called by the CFSSL library, that has isCA = false as default (https://github.com/cloudflare/cfssl/blob/152152bec641f502651...)
Also it is verified that the CSR doesn't contain that field in Boulder: https://github.com/letsencrypt/boulder/blob/aa71088c440a63e1...
This test is called when you send the CA a CSR: https://github.com/letsencrypt/boulder/blob/08ac100788c7edaf...
I don't know for other CAs, but from that quick look of the code boulder doesn't seem to sign certificates that can sign other certificates.