This option determines whether curl verifies the authenticity of the peer's certificate. A value of 1 means curl verifies; 0 (zero) means it doesn't.
When negotiating a TLS or SSL connection, the server sends a certificate
indicating its identity. Curl verifies whether the certificate is authentic,
i.e. that you can trust that the server is who the certificate says it is.
This trust is based on a chain of digital signatures, rooted in certification
authority (CA) certificates you supply. curl uses a default bundle of CA
certificates (the path for that is determined at build time) and you can
specify alternate certificates with the
#CURLOPT_CAINFO option or the
#CURLOPT_SSL_VERIFYPEER is enabled, and the verification fails to
prove that the certificate is authentic, the connection fails. When the
option is zero, the peer certificate verification succeeds regardless.
Authenticating the certificate is not enough to be sure about the server. You
typically also want to ensure that the server is the server you mean to be
talking to. Use
#CURLOPT_SSL_VERIFYHOST for that. The check that the
host name in the certificate is valid for the host name you're connecting to
is done independently of the
WARNING: disabling verification of the certificate allows bad guys to man-in-the-middle the communication without you knowing it. Disabling verification makes the communication insecure. Just having encryption on a transfer is not enough as you cannot be sure that you are communicating with the correct end-point.
NOTE: even when this option is disabled, depending on the used TLS backend,
curl may still load the certificate file specified in
#CURLOPT_CAINFO. curl default settings in some distributions might use
quite a large file as a default setting for
loading the file can be quite expensive, especially when dealing with many
connections. Thus, in some situations, you might want to disable verification
fully to save resources by setting
Nil - but
please also consider the warning above!