Add a site column into content type SharePoint 2013 using csom PowerShell

AddField-InContentType.ps1

Try{
    #Loading SharePoint Client side namespaces
    Add-Type -Path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.dll'
    Add-Type -Path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.Runtime.dll'
    Add-Type -Path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.Publishing.dll'
    Add-Type -Path 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\ISAPI\Microsoft.SharePoint.Client.Taxonomy.dll'
}

catch {
	Throw "Unable to load SharePoint Client runtime"
}


function AddField-InContentType()
{
    param(
        [Parameter(Mandatory=$true)][string]$url,
        [Parameter(Mandatory=$false)][System.Net.NetworkCredential]$credentials,
        [Parameter(Mandatory=$true)][string]$ContentTypeName,
        [Parameter(Mandatory=$true)][string]$FieldInternalName
    )
    
    begin{
        try
        {
            #Get Client Object
	    #
            $Context = New-Object Microsoft.SharePoint.Client.ClientContext($url) 
            $Context.Credentials = $Credentials 

            #Load web, fields and site objects
            #
            $web = $Context.Web
            $fields = $Context.Site.RootWeb.Fields;         
            $site = $context.Site 
            $Context.Load($web)
            $Context.Load($site)
            $Context.Load($fields)
            $Context.ExecuteQuery()

        }
        catch
        {
            Write-Host "Error while getting context. Error -->> "  + $_.Exception.Message -ForegroundColor Red
        }
    }
    process{
        try
        {
	    #Check whether site column exists in site collection columns
	    #
            Write-Host "Check if the site column" $FieldInternalName "is exist or not" -ForegroundColor Cyan 
            try
            {
                $field = $fields.GetByInternalNameOrTitle($FieldInternalName)
                $Context.Load($field)
                $Context.ExecuteQuery()
                Write-Host "Site column" $FieldInternalName "exist" -ForegroundColor Cyan
            }
            catch
            {
                Write-Host "Site column" $FieldInternalName " does not exist in the list of site collection columns" -ForegroundColor Cyan
                return
            }

	    #Getting content types from the root site
	    #
            $contentTypes = $Context.Site.RootWeb.ContentTypes
            $Context.Load($contentTypes)
            $Context.ExecuteQuery()
			
	    #Getting specified content type in which we need to add a column
	    #
            $contentType = $contentTypes | Where {$_.Name -eq $ContentTypeName}

            #Get Fields from the content type
	    #
            $fieldCollection = $contentType.Fields
            $Context.Load($fieldCollection);
            $Context.ExecuteQuery();

            #Check if field already exists in content type or not
            #
            $IsFieldExists = $false
            foreach($fld in $fieldCollection)
            {
                Write-Host $fld.get_InternalName()
                if($fld.get_InternalName() -eq $FieldInternalName){
                    $IsFieldExists = $true
                }
            }
            

            if($IsFieldExists -eq $false)
            {
                #Get all the columns associated with content type
		#
                $fieldRefCollection = $contentType.FieldLinks;
                $Context.Load($fieldRefCollection);
                $Context.ExecuteQuery();
                
                #Add a new column to the content type
		#
                Write-Host "Adding site column " $FieldInternalName "to the content type" -ForegroundColor Cyan
                $fieldReferenceLink = New-Object Microsoft.SharePoint.Client.FieldLinkCreationInformation
                $fieldReferenceLink.Field = $field;
                $contentType.FieldLinks.Add($fieldReferenceLink);
                
                
                $contentType.Update($true)
                $Context.Load($contentType)
                $Context.ExecuteQuery()
                
                Write-Host "Field added successfully" -ForegroundColor Green
            }
            else
            {
                Write-Host "Site Column " $FieldInternalName " already exists in content type" -ForegroundColor Cyan
            }
        }
        catch
        {
            Write-Host ("Error while adding field in contet type. Error -->> " + $_.Exception.Message) -ForegroundColor Red
        }
    }
    end{
        $Context.Dispose()
    }

    
}


$credentials = Get-Credential
$Url = 'http://YourSite.com'

AddField-InContentType $Url $credentials "Your Content Type Name" "YourSiteColumn"