Trying to debug a .NET Core app as a different user

I’m working on a .NET Core console app at work that, on one level, is pretty simple. It’s just calling a couple of web services, getting results back, combining/filtering them, and outputting some JSON files. (Eventually, in theory, it’ll also be sending those files to somebody via SFTP. But not yet.)

There have been a bunch of little issues with this project though. One issue is that one of the web services I’m calling uses AD for auth, and my normal AD account doesn’t have access to it. (This is the SOAP web service I blogged about last week.) So I have to access it under a different account. It’s easy enough to do that when I’m running it in production, but for testing and debugging during development, it gets a little tricky. I went down a rabbit hole trying to find the easiest way to deal with this, and thought it might be worthwhile to share some of my work.

In Visual Studio, I would normally debug a program just by pressing F5. That will compile and run it, under my own AD account, obviously. My first attempt at debugging this app under a different user account was to simply launch VS 2017 under that account. That’s easy enough to do, by shift-right-clicking the icon and selecting “run as different user”. But then there are a host of issues, the first being that my VS Pro license is tied to my AD/AAD account, so launching it as a different user doesn’t use my license, and launches it as a trial. That’s OK short-term, but would eventually cause issues. And all VS customization is tied to my normal user account, so I’m getting a vanilla VS install when running it that way. So that’s not really a good solution.

My next big idea was to use something like this Simple Impersonation library. The idea being to wrap my API calls with this, so they’d get called under the alternate user, but I could still run the program under my normal account. But the big warning in the README about not using impersonation with async code stopped me from doing that.

So, at this point, I felt like I’d exhausted the ideas for actually being able to run the code under the VS debugger and dropped back to running it from a command-line. This means I’m back to the old method of debugging with Console.WriteLine() statements. And that’s fine. I’m old, and I’m used to low-tech debugging methods.

So the next thing was to figure out the easiest way to run it from the command-line under a different user account. I spent a little time trying to figure out how to open a new tab in cmder under a different account. It’s probably possible to do that, but I couldn’t figure it out quickly and gave up.

The next idea was to use this runas tool to run the program as the alternate user, but still in a PowerShell window running under my own account. I had a number of problems with that, which I think are related to my use of async code, but I didn’t dig too deeply into it.

So, eventually, I just dropped back to this:

Start-Process powershell -Credential domain\user -WorkingDirectory (Get-Location).Path

This prompts me for the password, then opens up a new PowerShell window, in the same folder I’m currently in. From there, I can type “dotnet run” and run my program. So maybe not the greatest solution, but I’d already spent too much time on it.

One more thing I wanted to be able to do was to distinguish my alternate-user PowerShell session from my normal-user PowerShell session. I decided to do that with a little customization of the PS profile for that user. I’d spent some time messing with my PowerShell profile about a month ago, and documented it here. So the new profile for the alternate user was based on that. I added a little code to show the user ID in both the prompt and the window title. Here’s the full profile script:

function prompt {
    $loc = $(Get-Location).Path.Replace($HOME,"~")
    $(if (Test-Path variable:/PSDebugContext) { '[DBG]: ' } else { '' }) +
    "[$env:UserName] " +
    $loc +
    $(if ($NestedPromptLevel -ge 1) { '>>' }) +
    $(if ($loc.Length -gt 25) { "`nPS> " } else { " PS> " })
$host.ui.RawUI.WindowTitle = "[$env:UserName] " + $host.ui.RawUI.WindowTitle

You can see that I’m just pulling in the user ID with $env:UserName. So that’s that.

I’m not sure if this post is terribly useful or coherent, but it seemed worthwhile to write this stuff up, since I might want to reference it in the future. I probably missed a couple of obvious ways of dealing with this problem, one or more of which may become obvious to me in the shower tomorrow morning. But that’s the way it goes.

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