# Setup context
$context=New-Object Microsoft.SharePoint.Client.ClientContext($siteUrl)
$web=$context.Web

# New user object
$user=$web.EnsureUser("domainusername");

# Role definition
$rd = $web.RoleDefinitions.GetByName("Full Control")

# Create role definition binding collection
$rdbc=New-Object Microsoft.SharePoint.Client.RoleDefinitionBindingCollection($context)
$context.ExecuteQuery();
$rdbc.Add($rd)

$context.Web.RoleAssignments.Add($user, $rdbc)

$context.ExecuteQuery();

public void Load<T>(
    T clientObject,
    params Expression<Func<T, Object>>[] retrievals
)
where T : ClientObject

class Program
    {
        static void Main(string[] args)
        {
            ClientContext ctx = new ClientContext("http://domain-dev/");
            Web web = ctx.Web;
            ctx.Load(web);
            ctx.ExecuteQuery();
            Console.WriteLine(web.Title);

            User user = web.EnsureUser("domain\bdobbs");
            ctx.Load(user);
            ctx.ExecuteQuery();

            Console.WriteLine(user.Email);

            var rd = web.RoleDefinitions.GetByName("Full Control");
            ctx.Load(rd);
            ctx.ExecuteQuery();

            Console.WriteLine(rd.Description);

            RoleDefinitionBindingCollection rdbc = new RoleDefinitionBindingCollection(ctx);
            ctx.Load(rdbc);
            ctx.ExecuteQuery();

            rdbc.Add(rd);
            web.RoleAssignments.Add(user, rdbc);
            web.Update();
            ctx.ExecuteQuery();

            Console.Read();


        }
    }

# Setup context
$context=New-Object Microsoft.SharePoint.Client.ClientContext($siteUrl)
$web=$context.Web

//Load the $web object here.

# New user object
$user=$web.EnsureUser("domainusername");

//load the $user object here.

# Role definition
$rd = $web.RoleDefinitions.GetByName("Full Control")

# Create role definition binding collection
$rdbc=New-Object Microsoft.SharePoint.Client.RoleDefinitionBindingCollection($context)

//load the $rdbc object here.

$context.ExecuteQuery();

$rdbc.Add($rd)

$context.Web.RoleAssignments.Add($user, $rdbc)

$context.ExecuteQuery();

Add-Type -Path "C:Program FilesCommon Filesmicrosoft sharedSharePoint ClientMicrosoft.SharePoint.Client.dll"
Add-Type -Path "C:Program FilesCommon Filesmicrosoft sharedSharePoint ClientMicrosoft.SharePoint.Client.Runtime.dll"

$Ctx = New-Object Microsoft.SharePoint.Client.ClientContext("SharePointSiteURL")

$Web = $Ctx.Web

$Ctx.Load($Web)
$Ctx.ExecuteQuery()
Write-Host $Web.Title

$User = $Web.EnsureUser("domainUserID")
$Ctx.Load($User)
$Ctx.ExecuteQuery()
Write-Host $User.Email

$RD = $Web.RoleDefinitions.GetByName("Full Control")
$Ctx.Load($RD)
$Ctx.ExecuteQuery()
Write-Host $RD.Description

$RDBC = New-Object Microsoft.SharePoint.Client.RoleDefinitionBindingCollection($Ctx)
$Ctx.Load($RDBC)
$Ctx.ExecuteQuery()

$RDBC.Add($RD)
$ctx.Load($Web.RoleAssignments.Add($User, $RDBC))
$Web.Update()
$Ctx.ExecuteQuery()