The solution is to add the Web Gateway certificate into the cacerts file of JRE used by ITCM tomcat.
1- Do a copy of file C:\Program Files (x86)\CA\SC\JRE\1.8.0_60\lib\security\cacerts as cacerts.ori
Remarks :
Adapt the path with the installation path of ITCM.
In ITCM 14, JRE version used is 1.8.0_60 but it may be change in future version.
2- Get an export file of the missing certificate.
Ask security team for an export of missing certificate.
or
If the certificate has already been imported in Windows it could be exported using mmc.
Follow the steps described in this Microsoft page in order to display the certificates in mmc :
Then certificate could be exported in a .cer file by right-clicking on it and choose All Tasks - Export... :
3- Execute this in a Command Prompt in order to import the missing certificate into JRE cacerts :
cd c:\Program Files (x86)\CA\SC\JRE\1.8.0_60\bin
keytool -import -alias aliasname -keystore "<..\lib\security\cacerts>" -file "certificate_file"
The password for keystore is by default : changeit
4- Then restart tomcat & IIS :
Caf stop tomcat
Iisreset
Caf start tomcat