Send GET request to the SharePoint API using interactive login with username and password for use with in example the Site Manager API

Send-CorpSharePointGetRequest.ps1

function Send-CorpSharePointGetRequest
{
    Param(
        [Parameter(Mandatory=$true)]
        [string]$Url,
        [Parameter(Mandatory=$true)]
        [string]$UserName,
        [Parameter(Mandatory=$true)]
        [System.Security.SecureString]$Password,
        [Parameter(Mandatory=$true)]
        [string]$RequestUrl
    )

    $Result = $null

    try
    {
        $Context = New-Object Microsoft.SharePoint.Client.ClientContext($Url)
        $Context.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Username, $Password)
        $Context.ExecuteQuery()

        $RequestUrl = "$($Url)$($RequestUrl)"
        $AuthenticationCookie = $Context.Credentials.GetAuthenticationCookie($Url, $true)

        $WebSession = New-Object Microsoft.PowerShell.Commands.WebRequestSession
        $WebSession.Cookies.SetCookies($Url, $AuthenticationCookie)
        $WebSession.Headers.Add("Accept", "application/json;odata=verbose")

        $Result = Invoke-RestMethod -Method Get -WebSession $WebSession -Uri $RequestUrl

        $Context.Dispose()        
    }
    catch
    {
        Write-Output "Error when getting data from SharePoint (GET): $($_.Exception.Message)"
    }

    return $Result
}