new-jwt.ps1

function New-JWT (
    [Parameter(Mandatory = $True)]
    [ValidateSet("HS256", "HS384", "HS512")]
    $Algorithm = "HS256",
    $type = "JWT",
    [Parameter(Mandatory = $True)]
    [string]$Issuer = $null,
    [int]$ValidforMinutes = 10,
    [string]$Name = $null,
    [Parameter(Mandatory = $True)]
    $PrivateKey = $null
) {

    $exp = [int][double]::parse((Get-Date -Date $((Get-Date).addminutes($ValidforMinutes).ToUniversalTime()) -UFormat %s))

    [hashtable]$header = @{alg = $Algorithm; typ = $type}
    [hashtable]$payload = @{iss = $Issuer; exp = $exp}

    $headerjson = $header | ConvertTo-Json -Compress
    $payloadjson = $payload | ConvertTo-Json -Compress
    
    $headerjsonbase64 = [Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes($headerjson)).Split('=')[0].Replace('+', '-').Replace('/', '_')
    $payloadjsonbase64 = [Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes($payloadjson)).Split('=')[0].Replace('+', '-').Replace('/', '_')

    $ToBeSigned = $headerjsonbase64 + "." + $payloadjsonbase64

    $SigningAlgorithm = switch ($Algorithm) {
        "HS256" {New-Object System.Security.Cryptography.HMACSHA256}
        "HS384" {New-Object System.Security.Cryptography.HMACSHA384}
        "HS512" {New-Object System.Security.Cryptography.HMACSHA512}
    }

    $SigningAlgorithm.Key = [System.Text.Encoding]::UTF8.GetBytes($PrivateKey)
    $Signature = [Convert]::ToBase64String($SigningAlgorithm.ComputeHash([System.Text.Encoding]::UTF8.GetBytes($ToBeSigned))).Split('=')[0].Replace('+', '-').Replace('/', '_')
    
    $JWT = "$headerjsonbase64.$payloadjsonbase64.$Signature"

    $JWT
}