You may know that it’s a best practice to validate arguments you pass to your function.

For example, if you want to validate that your parameter named MyString is not null nor empty you can use the ValidateNotNullOrEmpty attribute.

function Foo
{
    Param([ValidateNotNullOrEmpty()]$MyString)

    #Doing some stuff
}

But there are other validations which must be done through casting¹ or type accelerators. And fortunately, there is data type dedicated to credentials, which is simply named PSCredential.

For example:

function Foo
{
    Param([PSCredential]$Credential)

    #Doing some stuff
}

More about

• Functions Advanced Parameters (MSDN)

• Simplify Your PowerShell Script with Parameter Validation (Scripting Guy)

• Working with type accelerators in PowerShell (Jaap Brasser)

• Casting Values in Powershell (Powershell Atoms)