Convert a string to Base64

ConvertTo-Base64.ps1

using namespace System.Management.Automation
using namespace System.Text

class EncodingTransformAttribute : ArgumentTransformationAttribute {

    [object] Transform([EngineIntrinsics]$engineIntrinsics, [object] $inputData) {
        
        switch ($inputdata) {
            { $_ -is  [System.Text.Encoding]} {

                return $_
            }

            { $_ -is [String]} {
                if ( $_ -in ([Encoding] | Get-Member -Static -MemberType Property).Name ) {
                  return [System.Text.Encoding]::$_
                }
                elseif ($_ -in [System.Text.Encoding]::GetEncodings().Name) {

                    return [System.Text.Encoding]::GetEncoding($_)
                }
            }
        }
        
        throw [ArgumentTransformationMetadataException]::new()
    }
}

function ConvertTo-Base64 {
    <#
        .SYNOPSIS
        Converts a human-readable string to Base64

        .PARAMETER String
        The string to encode in Base64

        .EXAMPLE
        ConvertTo-Base64 -String "The lazy log floats in the river"

        .EXAMPLE
        "Some people just like to watch the world burn" | ConvertTo-Base64

    #>
    [cmdletBinding()]
    param(
        [Parameter(Mandatory,ValueFromPipeline,ValueFromPipelineByPropertyName)]
        [String]
        $String,

        [Parameter()]
        [ArgumentCompleter(
            {
                param($Command, $Parameter, $Encoding, $CommandAst, $FakeBoundParams)
                $ValidEncodings = ([Encoding] | Get-Member -Static -MemberType Property).Name + [System.Text.Encoding]::GetEncodings().Name | Sort-Object
                
                if(!$Encoding){
                    return $ValidEncodings
                }
                else {
                    return $ValidEncodings.Where{ $_.StartsWith($Encoding) }
                }
            }
        )]
        [EncodingTransformAttribute()]
        [Encoding]
        $Encoding
    )

    begin {}

    process {
    
        $Bytes = $Encoding.GetBytes($String)
        $EncodedText =[Convert]::ToBase64String($Bytes)
        $EncodedText
    
    }

    end {}
}