DNS Lookup failed show invalid certificate

[coom]

Hello,

I'm currently using a FortiGate 200D (FW 5.2) in my work environnement. As a security measure, we have implemented a PKI and successfully signed our management web interface of the FortiGate with our PKI.

Now, we would like to prevent certificate warning from being presented to our users by our webfilter policy. We created an Issuing CA certificate that is capable of signing other websites, but when an user ask for a website for which the DNS does not exist (ex : oazjdaopzjdazopjdazopjdqopsoqpsj.com), they see a warning from the FortiGate that said :

"The webserver reported that an error occurred while trying to access the website. Please click here to return to the previous page."

Our problem is that page is signed by the "Fortigate_CA_SSLProxy" which is an autosigned one, and so we see Chrome warnings.

Is there a way to replace this signing certificate with our real one ?

When I go to "System => Certificate" the Fortigate_CA_SSLProxy has 0 refs, so it's seems it's not used .. I don't understand where I can change this behaviour.

Thanks in advance,

Guillaume T.