OpenTC Development
Contents
Automatic login
The Remote Desktop Connection (mstsc.exe) client has the ability to automatically login without promping for credentials, when these are previously saved.
Credentials also can be added by using cmdkey.exe, which OpenTC uses to 'pass down' the credentials entered in it's login form.
Official documentation states that the correct way to use cmdkey.exe to save credentials for "Remote Access" is to use the /generic parameter instead of /add.
However, the RDC client adds saved credentials as a "Windows Credential" (/add) and not a generic one. In practice runs there seems to be no difference in results.
The "TERMSRV/" prefix to the target name exists to distinguish between user or gateway credentials.
Not using this prefix will result in authentication failure in an uncommon scenario where these credentials are different on the same server.
For security reasons, the credentials need to be removed as soon as possible after the connection has been established.
Requirements
In order for this to work smoothly, the RDP file and remote computer need to be configured to allowed for saved credentials.
RDP File
"Allow me to save credentials" must be checked (when credentials are saved, this text will change to "Always ask for credentials", which in that case must be unchecked).
prompt for credentials:i:0
When a gateway is used, "Use my RD Gateway credentials for the remote computer" must be checked (located in Advanced > Settings).
This is so that Remote Desktop knows the credentials for the remote computer are the same as the credentials for the gateway, so it will not ask for them a second time.
promptcredentialonce:i:1
Client Computer
The following Group Policy must not be enabled on the client computer:
Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Connection Client > "Prompt for credentials on the client computer"
Remote Computer
The following Group Policy must not be enabled on the remote computer:
Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Security > "Always prompt for password upon connection"
Notes
It is reported that the following registry value would overwrite the "Allow me to save credentials" option for RDP files:
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Terminal Services] "fPromptForPassword"=dword:00000000
Certificate/publisher warning
When there is no valid certificate, the Remote Desktop client will show a popup before connecting telling the user the identity of the remote computer or publisher cannot be verified.
This popup can be ignored to continue, however this would be an inconvenience to the end user and might give them a wrong impression.
Years ago there used to be the ability to set a registry value telling the client to skip this check, however Microsoft patched this since they considered it a security risk.
We recommend that you setup your Remote Desktop Session Host, Connection Broker, Gateway, and RDP file the correct way.
Checking the "Don't ask me again for connections to this computer" box will create a value in the key "HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client\LocalDevices", with the name of the remote computer.
When using a custom RD Gateway server name, a different value will be created with both the computer name and server name separated by a semicolon (;).
The data of this value is an add up on what features in "Local Resources" are selected, here is a list of affected features;
| Setting | File Value | Data |
|---|---|---|
| Record from this computer | "audiocapturemode:i:1" | 128 |
| Printers | "redirectprinters:i:1" | 64 |
| Clipboard | "redirectclipboard:i:1" | 4 |
| Ports | "redirectcomports:i:1" | 2 |
| Drives | "drivestoredirect:s:" (anything but empty) | 1 |
| Other supported PnP devices | "devicestoredirect:s:*" | 32 |
Having none of these features selected will result in the data of 0, but still requires the existence of the value. Having them all selected makes it 231.
Server mode
Without server mode, OpenTC is not able to check if a user has entered an incorrect password. Therefore when standalone mode is used and an incorrect password has been entered, the user will be prompted with Remote Desktop's own credential input form. This could have been avoided by creating a trigger when this form is being opened, whoever this requires Administrator right, something that we do not want to give the OpenTC local user account.
Letting the client directly check via Active Directory was also not considered as an option, mainly because it would require working credentials to check AD in the first place, plus it would require plugins and a lot of code.
When server mode is used, the client will first send the credentials to the OpenTC server, the server will check the credentials against Active Directory, and will do other check like whether the account has been disabled locked or expired, or when the password has expired. When the latter is the case the server will return this to the client and the client will show a popup screen to change the password, which in turn will be send back to the server for them to be changed.
