Auto-Opening RDP files for each Client OS

Windows

Windows will query Group Policy to determine whether it should prompt the user for verification when opening an RDP connection. There are also configuration options for individual browsers that cause the browser to launch the RDP connection immediately after the RDP configuration file download completes.

Kasm automatically generates a signed RDP file using the certificate and private key in Server Settings. To avoid Windows warning that the Kasm RDP file is provided by an untrusted/unknown publisher, you must do the following:

1. Install either the certificate generated by Kasm or an applicable CA certificate on the client machine in the trusted certificate store.
2. Add the SHA1 thumbprint of the certificate as a trusted RDP publisher in Group Policy.

To make things easier, Kasm provides a button to download the certificate and a button to copy the SHA1 thumbprint to your clipboard in order to add to your group policy.

RDP Public Signing Certificate

The location in Group Policy is Computer Configuration -> Administrative Templates -> Windows Components -> Remote Desktop Services -> Remote Desktop Connection Client -> Specify SHA1 thumbprints of certificates representing trusted .rdp publishers.

Group Policy Location

Setting the Trusted Publisher Certificate SHA1

To prevent a user from modifying a signed RDP file and then attempting to create a connection to the RDP target, there is another group policy setting that can be enabled: Computer Configuration -> Administrative Templates -> Windows Components -> Remote Desktop Services -> Remote Desktop Connection Client -> Allow .rdp files from unknown publishers.

info

This GPO setting has the side effect of preventing a user from opening any RDP file not signed by a verified publisher, including those created by the user.

Deny unknown publishers

Google Chrome

Option 1

The user right-clicks the rdp file in the download list and selects Always open files of this type.

Always Open Files of this Type

Option 2

The user or an administrator sets a registry entry.

• Registry Key: Software\Policies\Google\Chrome\AutoOpenFileTypes
• Registry Subkey: An index number
• Registry Value: A file extension

For example: Software\Policies\Google\Chrome\AutoOpenFileTypes\1 = rdp.

Firefox

When right-clicking the RDP file download, the option Always Open Similar Files sets Firefox to automatically open RDP files in the default client.

Always Open Similar Files

ChromeOS

The Chromebook (or other host running ChromeOS) must be joined to a Google Workspace Enterprise account. The administrator can set Chrome managed policies to ensure that Chrome will automatically open the RDP file upon download.

Google Workspace configuration

1. Log into the Google Workspace account at admin.google.com.
2. Navigate to Devices -> Chrome -> Settings.

ChromeOS device settings

3. Select the User & browser settings tab.
4. Scroll down to the Content section and select Auto open downloaded files.

ChromeOS device content settings

5. Add RDP to the Auto open file types. The administrator can also restrict this setting to the URL of the Kasm deployment, e.g. https://kasm.example.com/*.

ChromeOS Auto open downloaded files settings

MacOS

On macOS the RDP connection is loaded as a URL rather than a downloadable file. An RDP client that supports the rdp:// URL scheme (such as Microsoft Remote Desktop) must be installed.

Google Chrome

By default Chrome will show a confirmation dialog each time an rdp:// URL is opened. To have Chrome automatically launch the RDP client without the dialog, set the AutoLaunchProtocolsFromOrigins policy. Replace https://kasm.example.com with your Kasm deployment URL:

defaults write com.google.Chrome AutoLaunchProtocolsFromOrigins -array '{ protocol = rdp; allowed_origins = ("https://kasm.example.com"); }'

note

Chrome must be fully restarted (not just the tab) for the policy to take effect. You can verify the policy is active by navigating to chrome://policy in Chrome.

Firefox

Create the distribution directory and policies file at /Applications/Firefox.app/Contents/Resources/distribution/policies.json. The file must be owned by root. Replace https://kasm.example.com with your Kasm deployment URL:

sudo mkdir -p "/Applications/Firefox.app/Contents/Resources/distribution"
sudo tee "/Applications/Firefox.app/Contents/Resources/distribution/policies.json" << 'EOF'
{
  "policies": {
    "AutoLaunchProtocolsFromOrigins": [
      {
        "protocol": "rdp",
        "allowed_origins": [
          "https://kasm.example.com"
        ]
      }
    ]
  }
}
EOF
sudo chown -R root:wheel "/Applications/Firefox.app/Contents/Resources/distribution"

note

Firefox must be fully restarted for the policy to take effect. You can verify the policy is active by navigating to about:policies in Firefox.

Safari

Safari does not provide an enterprise policy or command-line setting to suppress the external protocol confirmation dialog. On the first rdp:// URL launch Safari will prompt the user to allow the RDP client to open. For MDM-managed devices a configuration profile can be deployed to allowlist the rdp:// URL scheme.