public/Get-TokenViaClientCertificate.ps1
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<#
.SYNOPSIS The command implements client_credentials token request via client certificate. .DESCRIPTION The command implements client_credentials token request. More information: https://learn.microsoft.com/en-us/azure/active-directory/develop/v2-oauth2-client-creds-grant-flow .PARAMETER TenantID Entra ID Tenant ID, where authentication should take place. Default value: None Mandatory: Yes .PARAMETER ClientID Entra ID registered application ID (client ID). Default value: None Mandatory: Yes .PARAMETER Certificate X509Certificate2 object stored in windows store. Make sure the underlying CSP supports SHA2 (such as Microsoft Enhanced RSA and AES Cryptographic Provider) Default value: None Mandatory: Yes .PARAMETER PfxCertificate Path to certificate and private key stored in PKCS#12 envelope. Default value: None Mandatory: Yes .PARAMETER Password Path to password to PKCS#12 file. Default value: None Mandatory: Yes .PARAMETER Scopes Requested OAuth scopes. Default value: .default Mandatory: No .NOTES Author : Martin Rublik (martin.rublik@bspc.sk) Created : 2024-02-05 Version : 1.0 Changelog: V 1.0 (2023-10-24) - intial version V 1.1 (2024-02-05) - added support for client certificate calls License: The MIT License (MIT) Copyright (c) 2016 Martin Rublik Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. Inspired by: PKCS#12 correct CSP selection, cumbersome but works https://stackoverflow.com/questions/45084515/update-x509certificate2-with-correct-cryptographic-service-provider-in-bouncy-ca JWT creation: https://stackoverflow.com/questions/73673368/powershell-code-to-implement-client-credential-authentication-using-self-signed .EXAMPLE $token = Get-TokenViaClientCertificate -TenantID '198a560e-d60c-450e-b801-f11cf700c193' -ClientID 'b7260572-0f8b-43cb-b45d-a86e3dcb645b' -Certificate (ls Cert:\CurrentUser\my\25b100eb723374e0c28255cccda93e06221eed9f) Requests a token via client_credential flow (mostly used for system-2-system access). Default scope (.default) is used. .EXAMPLE $token = Get-TokenViaClientCertificate -TenantID "4e549187-9eea-4eb9-80a3-58a43b8f0ed7" -ClientID 'b7260572-0f8b-43cb-b45d-a86e3dcb645b' -PfxCertificate 'C:\data\onedrive\OneDrive - BSP Consulting\Desktop\ED-selfSigned-Cert2.pfx' -Password '1234' Requests a token via client_credential flow (mostly used for system-2-system access). Default scope (.default) is used. #> function Get-TokenViaClientCertificate { [cmdletbinding(ConfirmImpact = 'Low')] param( [Parameter(Mandatory=$true,ValueFromPipeline = $false)] [string] $TenantID, [Parameter(Mandatory=$true,ValueFromPipeline = $false)] [string] $ClientID, [Parameter(Mandatory=$true,ValueFromPipeline = $false,ParameterSetName="CertFromStore")] [System.Security.Cryptography.X509Certificates.X509Certificate2] $Certificate, [Parameter(Mandatory=$true,ValueFromPipeline = $false,ParameterSetName="CertFromFile")] [string] $PfxCertificate, [Parameter(Mandatory=$true,ValueFromPipeline = $false,ParameterSetName="CertFromFile")] [string] $Password, [Parameter(Mandatory=$false,ValueFromPipeline = $false)] [string[]] $Scopes=".default" ) try { # build URL for code request if ($Certificate) { $ClientCertificate=$Certificate $PrivateKey = [System.Security.Cryptography.RSACryptoServiceProvider]$ClientCertificate.PrivateKey } if ($PfxCertificate) { $ClientCertificate=new-object System.Security.Cryptography.X509Certificates.X509Certificate2($PfxCertificate, $Password, [System.Security.Cryptography.X509Certificates.X509KeyStorageFlags]::Exportable) $serialzed=$ClientCertificate.PrivateKey.ToXmlString($true) $cspParams = new-object System.Security.Cryptography.CspParameters $cspParams.ProviderName = "Microsoft Enhanced RSA and AES Cryptographic Provider" $cspParams.ProviderType = 24 $PrivateKey = New-Object System.Security.Cryptography.RSACryptoServiceProvider($cspParams); $PrivateKey.FromXmlString($serialzed) } #Create base64 hash of certificate ################################## $CertificateBase64Hash = [System.Convert]::ToBase64String($ClientCertificate.GetCertHash()) #Create JWT timestamp for expiration #################################### $StartDate = (Get-Date "1970-01-01T00:00:00Z" ).ToUniversalTime() $JWTExpirationTimeSpan = (New-TimeSpan -Start $StartDate -End (Get-Date).ToUniversalTime().AddMinutes(5)).TotalSeconds $JWTExpiration = [math]::Round($JWTExpirationTimeSpan,0) #Create JWT validity start timestamp #################################### $NotBeforeExpirationTimeSpan = (New-TimeSpan -Start $StartDate -End ((Get-Date).ToUniversalTime())).TotalSeconds $NotBefore = [math]::Round($NotBeforeExpirationTimeSpan,0) #Create JWT header ################# $JWTHeader = @{ alg = "RS256" typ = "JWT" x5t = $CertificateBase64Hash -replace '\+','-' -replace '/','_' -replace '=' } #Create JWT payload ################# $JWTPayLoad = @{ aud = "https://login.microsoftonline.com/$tenantId/oauth2/token" exp = $JWTExpiration iss = $ClientID jti = [guid]::NewGuid() nbf = $NotBefore sub = $ClientID } # Convert header and payload to base64 ################################# $JWTHeaderToByte = [System.Text.Encoding]::UTF8.GetBytes(($JWTHeader | ConvertTo-Json)) $EncodedHeader = [System.Convert]::ToBase64String($JWTHeaderToByte) $JWTPayLoadToByte = [System.Text.Encoding]::UTF8.GetBytes(($JWTPayload | ConvertTo-Json)) $EncodedPayload = [System.Convert]::ToBase64String($JWTPayLoadToByte) # Join header and Payload with "." to create a valid (unsigned) JWT ###################################################### $JWT = $EncodedHeader + "." + $EncodedPayload # Define RSA signature and hashing algorithm ##################################### $RSAPadding = [Security.Cryptography.RSASignaturePadding]::Pkcs1 $HashAlgorithm = [Security.Cryptography.HashAlgorithmName]::SHA256 # Create a signature of the JWT ######################### $Signature = [Convert]::ToBase64String( $PrivateKey.SignData([System.Text.Encoding]::UTF8.GetBytes($JWT),$HashAlgorithm,$RSAPadding) ) -replace '\+','-' -replace '/','_' -replace '=' # Join the signature to the JWT with "." ############################### $JWT = $JWT + "." + $Signature # Use the self-generated JWT as Authorization to get the Access Token ########################################################## $Header = @{ Authorization = "Bearer $JWT" } $Body = @{ client_id = $ClientID client_assertion = $JWT client_assertion_type = "urn:ietf:params:oauth:client-assertion-type:jwt-bearer" scope = $($Scopes -join " ") grant_type = "client_credentials" } #$authUri = "https://login.microsoftonline.com/common/oauth2/token" $authUri = "https://login.microsoftonline.com/$TenantID/oauth2/v2.0/token" $TokenResponse = Invoke-RestMethod -Header $Header -Uri $authUri -Method POST -Body $Body $TokenResponse }catch { throw $_ } } |