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  • Mucius 2 posts 92 karma points
    Jun 23, 2019 @ 16:30

    Umbraco forms login fails, if Azure App Service pre-authentication is enabled

    Good day,

    We've encountered very strange issue after deploying Umbraco to Azure App Service and enabling pre-authentication for it. Single Sign-On isn't enabled, so users have to authenticate twice: once to pass Azure AD pre-authentication, and once - on regular Umbraco login page.

    When pre-auth is off, the HTTP requests sent when a user submits his credentials are:

    1. POST request to /umbraco/backoffice/UmbracoApi/Authentication/PostLogin with 200 OK response,
    2. GET request to /umbraco/ServerVariables with 200 OK response.

    But when pre-authentication is enabled, then the 2nd request fails with 401 response and with text message You do not have permission to view this directory or page.

    Any idea what could cause this? How can I know whether this request hit Umbraco at all?

    Thanks, Mucius.

    Umbraco version: 7.5.4 assembly: 1.0.6136.27241

  • Mucius 2 posts 92 karma points
    Jul 03, 2019 @ 14:10


    Turns out, the EasyAuth mechanism used by Azure to provide pre-authentication for webapps isn't completely isolated from the webapps code:

    Solved by adding this environment variable to the webapp, on its Configuration --> Application settings page:


    Then the Thread.CurrentPrincipal ASP.Net variable used by Umbraco code isn't affected by the EasyAuth. As said here, "this is designed to allow developers to protect access to their site with auth, but still have it use a separate login mechanism within their app logic".

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