Base64 String converting in PowerShell because some frameworks trim the "=" at the end

base64.ps1

# source of functions: https://medium.com/@nikitafed9292/net-base64-decoding-workaround-82b797162b6e

# Add missing "=" at the end
Function Check-Base64 {

    param(
         [Parameter(Mandatory=$true)][String]$inputString
    )

    $input
    $encoded = $inputString.Replace('-','+').Replace('_','/')
    $d = $encoded.Length % 4
    if ( $d -ne 0 ) {
        $encoded  = $encoded.TrimEnd('=')
        if ( $d % 2 -gt 0 ) {
            $encoded += '='
        } else {
            $encoded += '=='
        }
    }
    return $encoded

}

# Remove "=" at the end
Function Trim-Base64 {

    param(
         [Parameter(Mandatory=$true)][String]$inputString
    )

    return $inputString.TrimEnd('=')

}


# Example
$payload = [ordered]@{
  "sub" = "1234567890"
  "name" = "John Doe"
  "iat" = 1516239022
}

$payloadBase64 = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes(($payload | ConvertTo-Json -Compress)),[Base64FormattingOptions]::None)
$payloadBase64Trimmed = Trim-Base64 -inputString $payloadBase64
$payloadBase64Checked = Check-Base64 -input $payloadBase64Trimmed

"input: $( $payloadBase64 )"
"trimmed: $( Trim-Base64 -inputString $payloadBase64 )"
"checked: $( Check-Base64 -input $payloadBase64Trimmed )"