ConvertFrom-SecureString

It looks like the issue might be related to how the client secret is being read and used in your script. Here are a few things to check and try:

1. Ensure the Client Secret is Correct:
   • Verify that the client secret stored in C:\temp\key.txt is correct and hasn’t expired. You can do this by generating a new client secret in the Azure portal and updating your text file.
2. Convert the Client Secret Properly:

• When reading the client secret from the file, ensure it is being converted correctly. You might need to use ConvertTo-SecureString with the -AsPlainText and -Force parameters if the secret is stored as plain text.
  1. Use the Correct Parameters:
     • Update your script to ensure the client secret is being passed correctly. Here is an example of how you might modify your script: $ClientId = "111111111111111111"

         `$ClientSecret = Get-Content "C:\temp\key.txt" | ConvertTo-SecureString -AsPlainText -Force`
       
         `$TenantId = "2222222222222222"`
       
         `$body = @{`
       
         `    client_id     = $ClientId`
       
         `    client_secret = [Runtime.InteropServices.Marshal]::PtrToStringAuto([Runtime.InteropServices.Marshal]::SecureStringToBSTR($ClientSecret))`
       
         `    tenant_id     = $TenantId`
       
         `    grant_type    = "client_credentials"`
       
         `}`
       

     $response = Invoke-RestMethod -Uri "https://login.microsoftonline.com/$TenantId/oauth2/v2.0/token" -Method Post -Body $body

1. Check for Typos:
   • Ensure there are no typos in your ClientId, ClientSecret, or TenantId.
2. Review Azure Documentation:
   • Refer to the Azure documentation for detailed steps on registering an app and using client credentials.