REST-API Basic Authentication and Invoke-WebRequest via Powershell

Question

Trying to connect to a REST-API via Powershell client. When testing the endpoint in Postman, I have no problems at all. Here's the main part of the function (I have a [pscredential]$Creds parameter that I use to get the username and password):

[string]$username = $Creds.UserName
[string]$password = (New-Object System.Net.NetworkCredential($Creds.UserName, $Creds.Password, 'Null')).Password
[string]$authorizationInfo= ([Convert]::ToBase64String([Text.Encoding]::ASCII.GetBytes(('{0}:{1}' -f $username, $password))))

Invoke-WebRequest -Uri "https://$($HostName)/api/" -Method Get -Headers @{Authorization = ('Basic {0}' -f $authorizationInfo)}

For some reason the Authorization header is different in my script than in Postman. I can even copy the Authorization header out of Postman and paste it into the -Headers parameter and everything works fine. I just don't see where I'm getting this wrong.

adamt8 · Accepted Answer · 2020-05-28 04:26:23Z

4

I can't tell you why that's not working, but I can suggest something that works for me all the time with APIs:

$auth = $username + ':' + $upassword
$Encoded = [System.Text.Encoding]::UTF8.GetBytes($auth)
$authorizationInfo = [System.Convert]::ToBase64String($Encoded)
$headers = @{"Authorization"="Basic $($authorizationInfo)"}

Invoke-WebRequest -Uri "https://$($HostName)/api/" -Method GET -Headers $headers

If that doesn't work, try this subtle difference with Invoke-Restmethod:

Invoke-RestMethod -Uri "https://$($HostName)/api/" -Method GET -Headers $headers

Working with APIs is always an adventure. Keep trying. :)

answered May 28, 2020 at 4:26

adamt8

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3 Comments

greatname Over a year ago

Thanks for the feedback. I'm getting the same issue with your snippet where the $authorizationInfo variable has a different Base64String than Postman (your value is the same value as my code) so it's not working. Since this value is "wrong" I'm getting an "The supplied credentials are invalid." message

greatname Over a year ago

Looks like you were right, this will be an adventure. It works fine, I just learned that the credential username is case sensitive!!

adamt8 Over a year ago

Every API seems to have its own quirks, and I wish there was a nice "lots of things to try" doc I could send you. Occasionally I get lucky and some new API just works, but usually there is a head-meets-wall session for a while. :)

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