OpenTC Development
Contents
Automatic login
The login screen where the credentials must be entered is a custom made form and is not related to any native Windows Remote Desktop functions.
Therefore, the credentials entered in the form must somehow be passed down to establish a Remote Desktop connection without having to fill in it's own credentials form.
There are two ways to do this, one of them is to make your own Remote Desktop client by using some Remote Desktop DLL's inside your project. This option has not been chosen for OpenTC, since in order to make all it's features available you would have to completely rewrite the client like the native one.
The other option is to fool Windows that the user has logged in before and used the "Remember me" option, causing it to automatically login without having to enter any credentials.
Before this can happen the credentials must be loaded into the current user, this can be done by using the built-in application cmdkey
Load credentials
Example on how Remote Desktop credentials would be saved:
cmdkey.exe /add:TERMSRV/<computername> /user:<username> /pass:<password>
It's important that "TERMSRV/" is placed before the computer or farm name, so Windows knows its destined for that connection.
When using a Remote Desktop Gateway (RD Gateway) the credentials must also be loaded separately for it, by using the gateway name;
cmdkey.exe /add:<gatewayname> /user:<username> /pass:<password>
The computernames and gatewaynames must be identical to the ones in the RDP-file, otherwise it will not work.
When the Remote Desktop connection has been established, it would be ideal to remove the saved credentials as soon as possible. OpenTC is being run under one local user account and therefore shares the same saved credentials database for anyone that uses the client computer.
While the following has not been reported as a bug in OpenTC, other Remote Desktop portal products who share this same method have incidentally experienced users being suddenly able to login to other users their account. We therefore take precaution and remove the credentials as soon as possible:
cmdkey.exe /delete:TERMSRV/<computername> cmdkey.exe /delete:<gatewayname>
Requirements
In order for this to work, the RDP-file would need to have a few settings set, this can by done with mstsc.exe or by opening the file with a text editor like Notepad.
"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
Some Group Policies must also be compliant. By default these are already set this way, however make sure this hasn't been changed.
On the client:
Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Connection Client > "Prompt for credentials on the client computer": Not Configured / Disabled
And on the host server:
Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Security > "Always prompt for password upon connection": Not Configured / Disabled
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 based on what features in "Local Resources" are selected, this is a list of affected features;
| Setting | File Value |
|---|---|
| Record from this computer | "audiocapturemode:i:1" |
| Printers | "redirectprinters:i:1" |
| Clipboard | "redirectclipboard:i:1" |
| Ports | "redirectcomports:i:1" |
| Drives | "drivestoredirect:s:" (anything but empty) |
| Other supported PnP devices | "devicestoredirect:s:*" |
Having none of these features selected will result in the data of 0, 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.
