(C++) Azure Key Vault Get OAuth2 Access Token using Client Credentials

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Demonstrates how to get an OAuth2 access token using client credentials for an Azure Key Vault resource.

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#include <CkHttp.h>
#include <CkHttpRequest.h>
#include <CkHttpResponse.h>
#include <CkJsonObject.h>

void ChilkatSample(void)
    {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // You can use OAuth2 client credentials with an Azure App (service principal) that has
    // the required Role-Based Access Control (RBAC) permissions.
    // In this case, it would be service principal with RBAC permissions to administer and manage
    // the key vault.

    // You can create the Azure App (also known as the Service Principal)
    // in the Azure CLI (command line interface) as follows:

    // ----------------------------------------------------------------------
    // az ad sp create-for-rbac --name http://example.com --role Contributor
    // ----------------------------------------------------------------------

    // The argument to --name must be a valid URI that is a verified domain of your 
    // organization or its subdomain.

    // The output of the above "az ad sp create-for-rbac ..." command is JSON such as this:

    // {
    //   "appId": "25ac6e3a-9ac7-42b9-b13e-18644c1de959",
    //   "displayName": "azure-cli-2023-10-14-22-38-15",
    //   "name": "http://example.com",
    //   "password": "f1f2f3f0-52dc-4236-8295-c8a1d6aa393c",
    //   "tenant": "4d8dfd66-68d1-13b0-af5c-b31b4b3d53d"
    // }

    // Save the values in the above JSON.  You'll need it below..

    // You'll also want to add the role of "Key Vault Administrator" to the Service Principal
    // for the particular key vault.

    // ----------------------------------------------------------------------
    // az role assignment create --assignee <Application-ID> --role "Key Vault Administrator" 
    //       --scope /subscriptions/<Subscription-ID>/resourceGroups/<Resource-Group-Name>/providers/Microsoft.KeyVault/vaults/<KeyVault-Name>
    // ----------------------------------------------------------------------

    CkHttp http;
    CkHttpRequest req;

    // Add query params to the request.
    req.AddParam("grant_type","client_credentials");

    // Use the service principal's appId
    req.AddParam("client_id","25ac6e3a-9ac7-42b9-b13e-18644c1de959");

    // Use the service principal's password.
    req.AddParam("client_secret","f1f2f3f0-52dc-4236-8295-c8a1d6aa393c");

    // Note: The resource must match the API for which you're using the access token..
    req.AddParam("resource","https://vault.azure.net");

    http.SetUrlVar("tenant","4d8dfd66-68d1-13b0-af5c-b31b4b3d53d");
    CkHttpResponse *resp = http.PostUrlEncoded("https://login.microsoftonline.com/{$tenant}/oauth2/token",req);
    if (http.get_LastMethodSuccess() != true) {
        std::cout << http.lastErrorText() << "\r\n";
        return;
    }

    const char *strRespBody = resp->bodyStr();
    int respStatusCode = resp->get_StatusCode();
    if (respStatusCode >= 400) {
        std::cout << "Response Status Code = " << respStatusCode << "\r\n";
        std::cout << "Response Body:" << "\r\n";
        std::cout << strRespBody << "\r\n";
        delete resp;
        return;
    }

    CkJsonObject jsonResp;
    jsonResp.Load(strRespBody);
    jsonResp.put_EmitCompact(false);
    std::cout << jsonResp.emit() << "\r\n";

    // The result is an access token such as the following:

    // {
    //   "token_type": "Bearer",
    //   "expires_in": "3600",
    //   "ext_expires_in": "3600",
    //   "expires_on": "1557864616",
    //   "not_before": "1557860716",
    //   "resource": "https://vault.azure.net",
    //   "access_token": "eyJ0eXAiOiJKV1QiL ... 20UFDDOHEyUg"
    // }

    // If you wish, you can save the token to a file.
    // The access token is generally valid for 1 hour.
    // After 1 hour, you would need to get a new access token in the same way.
    jsonResp.WriteFile("qa_data/tokens/azureKeyVaultToken.json");

    delete resp;
    }