We're having a play with SQL Server Master Data Services at MITIE with a view to using them to manage some of our analytical Master Data - currently done via scripting. One of the first challenges was security. There is a set of instructions here but we still managed to get stuck. We configured a user as an administrator for all models as described here but still got an "Access is Denied" message when trying to log in with that user. Note that the system administator has to be a user and not a group. The answer is elsewhere in the MSDN documentation;
Under User and Group Permissions click the down arrow > Edit > Functions. Here I'm showing the group page, but the user page works the same way:
Click the pencil icon to allow for editing
Add the functions as appropriate. These map onto the 'buttons' that are rendered in the MDS home-page, and should be self-explanatory. To add all of them simply click the button highlighted below:
Your user or group should now be able to log into MDS, with no "Access is Denied" message. Other permissions can be established as per the MSDN documentation.