NSS: client certificate not found (nickname not specified)?

Try prefixing the certificate filename with "./", or using the full path. From the curl manpage:

If curl is built against the NSS SSL library then this option [--cert] can tell curl the nickname of the certificate to use within the NSS database defined by the environment variable SSL_DIR (or by default /etc/pki/nssdb). If the NSS PEM PKCS#11 module (lib- nsspem.so) is available then PEM files may be loaded. If you want to use a file from the current directory, please precede it with "./" prefix, in order to avoid confusion with a nickname.

(emphasis mine)

Alternatively, some instructions for importing into the NSS certificate database are here, although I have not used them:http://rcritten.fedorapeople.org/nss_compat_ossl.html

I had the same issue on Centos 7. After debugging it was related to the the timeout.

So if you see this issue and use curl_setopt($curl, CURLOPT_TIMEOUT_MS, 300);Then check how long it takes. If it is around your timeout period. That is the problem and not related to any certificate.

I was expecting some timeout error from Curl in case of timeout but that doesn't seem to happen.

I got the same error message with curl when I entered the wrong password when trying to access a FTPS server which used simple password authentication. It had nothing to do with certificates.