This blog entry is a compilation of information that I have learned. I personally have not had the opportunity to access D3FO directly.
The Security Development Tool (SDT) that is in AX 2012 will no longer be available in Dynamics 365 for Operations (D3FO). Microsoft has taken some of the features of this tool and implemented it within the application as a part if the initial release. And they have intentions to release additional SDT features.
Gone from the D3FO Security menu is Security roles and Security privileges (see my unwrapped series - Explaining the Security Menu). It is now all part of the Security configuration menu item along with features of the Security development tool.
unwrapped series - Security Add-ins that required access to the AOT has now moved within the standard user interface. This is great news!!! You can now find all the roles, duties, privileges that have access to a specific menu or form with a file function. From a particular record or form, go to Options and select Security Diagnostics.
Check out Alex Meyer of Fastpath blog which has some additional details about the security features in D3FO. A big thank you goes out to Arbela and Corey Bakhtiary for putting on a webinar on February 8, 2017 to demonstrate the security functions in D3FO.