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CN=Sales,CN=Users,DC=test,DC=windows,DC=frevvo,DC=com 
CN=HR,CN=Users,DC=test,DC=windows,DC=frevvo,DC=com 
CN=Marketing,CN=Users,DC=test,DC=windows,DC=frevvo,DC=com

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That is not supported. You can only connect to one server.

How can I configure the

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Live Forms designers ?

The frevvo designers The  designers will be whatever members are returned by the LDAP filter configured in the property com.frevvo.security.ldap.frevvoDesignersFilter. It can essentially be any valid LDAP filter. One approach used by some customers is to created a group of frevvo designers  designers in LDAP (Active Directory for instance), associate members to that group using whatever client is typically used to manage the names in your organization and configure that group in frevvo . For instance:

<Parameter name="com.frevvo.security.ldap.frevvoDesignersFilter"   value="(memberOf=CN=FrevvoDesigners,CN=Users,DC=test,DC=windows,DC=frevvo,DC=com)" override="false"/>

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If cache is enabled (it is enabled by default), you may need to restart the frevvo server  server for the changes to take effect