Friday, 28 April 2017

Switch Master Page Minimum Permissions

Problem: Use the Client Side Object Model (CSOM C#) to add a new master pages to a site collection and switch the master page.

Initial Hypothesis: Writing to a site collection only required contribute rights or even "designer" rights at the web application permission level.

Resolution: The minimum permission set for changing master pages is "Full Permission" which a site owner and the site collection admin have.  So to switch master pages you need a high set of permissions.  UI allows master pages to be switched when the user only has "Design" permissions. This proof is flawed as the UI and CSOM permissions are different.  Can the UI have differnt permissions to the CSOM API???  Am I going mad.  
SPWeb object with Design user permissions cannot be updated and the API returns an "Access Denied Error" - Thanks to Sachin Khade for identifying this.

Summary: "Design" rights allow the user to change the master page using the UI however the same user cannot switch the master page using the CSOM C# approach.

Note: "Design" rights can be applied at the Web Application Policy level allowing the accounts with "Design" rights the ability to add master pages.  The "Design" permission is only built into SP at the Site Collection level, I created the "Design" permission with the same permissions at the web application level to ensure my account in the Web app Design group has access to all site collections on my web app.

Note: Microsoft do not recommend customized master pages for O365 or future development.  Rather inject JavaScript to modify pages.


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