Custom functions” typically refer to user-defined functions created by developers to perform specific tasks. 

Follow below steps to create attributes for Active Directory

• Login to Identity Bridge. 
• Go to Configuration Hub. 
• Go to Configure Source.  
• On the Active Directory tile click on the edit button. 
• Click on the Functions tab. 

To Add New Function 

• Login to Identity Bridge.   
• Go to Configuration Hub.   
• Go to Configure Source.    
• On the Active Directory Management tile click on the edit button.   
• Click on the Functions tab.   
• Click on Add New Function Button.   
• Add Function & Group window will open.   
• Select a group from drop down menu, more than one group can be added by clicking the Add Group Tab.   
• Enter a Function Name, more than one function name can be added by clicking the Add New Function Tab.   
• Click Update button.   
• That Function Name will be updated under Selected Group.