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

Send-CorpSharePointPostRequest.ps1

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

    $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)
        $FormsDigest = $Context.GetFormDigestDirect()

        $WebSession = New-Object Microsoft.PowerShell.Commands.WebRequestSession
        $WebSession.Credentials = $Context.Credentials
        $WebSession.Cookies.SetCookies($Url, $AuthenticationCookie)

        $Headers = @{ 
            'X-RequestDigest' = $FormsDigest.DigestValue;
            'odata-version' = '4.0' }

        if ($RequestBody -eq  $null)
        {
            $Result = Invoke-RestMethod -Method Post -WebSession $WebSession -Headers $Headers -ContentType "application/json;odata=verbose;charset=utf-8" -Uri $RequestUrl -UseDefaultCredentials
        }
        else
        {
            $Result = Invoke-RestMethod -Method Post -WebSession $WebSession -Headers $Headers -ContentType "application/json;odata=verbose;charset=utf-8" -Body $RequestBody -Uri $RequestUrl -UseDefaultCredentials
        }

        $Context.Dispose()        
    }
    catch
    {
        Write-Output "Error when posting data to SharePoint (POST): $($_.Exception.Message)"
    }

    return $Result
}