Test-CaptivePortal.ps1

Function Test-CaptivePortal {
<#
.SYNOPSIS
Tests internet connectivity using Microsoft's capitve portal test site. Returns $true if a captive portal is detected, otherwise false. 
 
.DESCRIPTION
Tests internet connectivity using Microsoft's capitve portal test site. Returns $true if a captive portal is detected, otherwise false. 
For more information on Windows Network Awareness, see
* https://docs.microsoft.com/en-us/windows-hardware/drivers/mobilebroadband/captive-portals 
* https://blog.superuser.com/2011/05/16/windows-7-network-awareness/

.PARAMETER Duration
Duration in seconds to continue testing. Minimum 1, Maximum 900
 
.INPUTS
<Inputs if any, otherwise state None>
 
.OUTPUTS
<Outputs if any, otherwise state None - example: Log file stored in C:\Windows\Temp\<name>.log>
 
.NOTES
Author: Andrew Zbikowski <andrew@itouthouse.com>
Change History: 
2018-11-27: Initial function development.
 
.EXAMPLE
if (-Not (Test-CaptivePortal -Duration 120)) {
    Write-Host "No Captive Portal Detected!"
    Invoke-WebRequest -Uri http://www.example.com
}

if (Test-CaptivePortal -Duration 90) {
    Write-Host "Captive Portal Detected! Use your web browser to log in." 
} else {
    Write-Host "No Captive Portal Detected!"
}

#>
    # Enable -Debug, -Verbose Parameters. Write-Debug and Write-Verbose!
    [CmdletBinding()]
    # Parameters 
    Param (
        [Parameter(Mandatory=$true,
            ValueFromPipeline=$false,
            Position=0,
            HelpMessage="Duration in seconds to continue testing. Minimum 1, Maximum 900")]
        [ValidateRange(1,900)]
        [int]$Duration
    )
    $count = 0
    Do {
        $count++
        $Result = Invoke-WebRequest -Uri http://www.msftncsi.com/ncsi.txt
        if ($Result.Content -eq "Microsoft NCSI") {
            Write-Verbose "Attempt $($count): it appears there is no captive portal."
            $false
            Break
        } else {
            Write-Verbose "Attempt $($count): it appears there is a captive portal."
            $true
            Start-Sleep -Seconds 1
        }
    } While ($count -lt $Duration)
}