How to list Azure VMs using the REST API with Oauth2?

Question

The Problem

MS Azure provides an extensive REST API. However, there is a significant amount of complexity when trying to get that API to work. From outdated and incomplete documentation to simple examples not working, performing what should be an easy task is instead nightmarish.

The Task

What are the exact, precise, detailed steps necessary to list the available VMs for someone who has logged in using Oauth2? For instance, this can be done using the azure-cli.

azure vm list

What are the steps to accomplish the same thing using REST and Oauth2?

The Requirements

The answer must not use Visual Studio, PowerShell, C#, an SDK, or any other such tool to accomplish this task. Only the portal is allowed for setup, and only Oauth2 is allowed for authorization, and only the REST API is allowed for actual information retrieval.

The answer must not simply link to external sources, although external references are encouraged for completeness.

The answer may assume the user has an Azure account. It must include information about creating the Oauth2 client, credentials, and any step necessary to get the appropriate token.

The answer must be detailed.

The answer must provide examples. Images, too are strongly encouraged.

The answer should include information about possible errors, their meanings, and what too look for to fix them.

Answer 1

Overview

Making requests against the Azure Rest API is a bit more complicated than perhaps you would think at first glance. In particular, there are a number of esoteric and not-so-helpful error messages you may run into while getting the nobs tweaked just right.

1. Introduction and Terms
2. Setting up The Application
3. Getting the access_token
4. Making the API request
5. Common errors thus far

Introduction and Terms

One of the pieces of this process that can make it so confusing and difficult is the terminology. Until you understand that, knowing how to deal with errors is very difficult. We'll go over some of the more common ones here.

Subscription - This is basically what you'd expect. It refers to the Microsoft Azure Services subscription. It basically acts as the top-level umbrella for the organization.

Tenant - This is like a sub-organization, maybe a department or group. There can be multiple tenants under a single subscription.

User - As expected, a user is a single individual. Users are scoped to tenants.

Application - The Application is the software program trying to use the API. It must be registered and configured to do so.

Service Principal - This is essentially The Application. It is the entity making API Service requests.

Setting Up the Application

Although you might not guess it, this is probably the most complicated part of the process. Let's start by creating The Application in the portal.

Create The Application

Follow this click path: Azure Active Directory -> App Registrations -> New

There should be a form for application creation, with the following fields:

• Name
  • This is simple the name of The Application. When authenticating, it will be shown to users. For the purposes of this "tutorial", we'll call it API Tutorial. This can be edited after creation.
• Application Type
  • The type of The Application. For our purposes, we should choose "Web app/API". This cannot be edited after creation.
• Sign-on URL
  • The is the redirect that will be used if we go the "authorization_code" route for sign on. This can be useful as the response will include an "id_token". We'll get into that a bit later. For now, let's make this http://123AzureApiTutorial.com/code. This can be edited after creation.

Once the Application has been created, you should see a property, Application ID. This is the client_id used in the OAuth2 flow. Take a note of its value.

Create the Client Secret

The OAuth2 flow requires a client secret value for authentication.

To generate it, follow this click path: Azure Active Directory -> App Registrations -> API Tutorial -> All Settings -> Keys Enter the key description: API Tutorial Key, and the Duration: In 1 year.

Click Save. This will generate the Key Value. You must copy the value here and save it somewhere. You will not have another opportunity to do so.

This value is the client_secret in the OAuth2 flow.

Add the correct permissions

To get to the permissions, follow this click path: Azure Active Directory -> App Registrations -> API Tutorial -> All Settings -> Required Permissions -> Add

Here you will see the list of possible APIs. The one we care about for Azure is Windows Azure Service Management API. There is currently only one permission: Access Azure Service Management as organization users (preview). Select it, click Select, and then Done.

Getting the access_token

The access_token is what allows us to make requests against the API. There are two primary ways to do this. I suggest reading about both before trying to implement them.

Authorization Code

The authorization code is a two-step process. First we obtain the authorization code, and then we use that to get the access_token. A benefit of this route is that we get back an id_token as well, with a variety of useful claims like the user's name, email address, etc.

The request format is as follows: (GET) https://login.microsoftonline.com/<tenant-id>/oauth2/authorize?client_id=<client-id>&scope=api&redirect_uri=<redirect-uri>&response_type=code&prompt=consent. Let's go over the parameters here really quick.

• Tenant ID
  • This can be obtained be using the click path Azure Active Directory -> Properties and copy the Directory ID. This is, in fact the Tenant ID value. It just has a different name to help with the overall confusion.
• Client ID
  • This is the Application ID we retrieved previously.
• Scope
  • This is the scope of the code. We just want to use the API.
• Redirect URI
  • This is the sign-on URL you specified when creating API Tutorial. After the user logs in, they will be redirected to this URL with a "code" parameter in the query string.
• Response Type
  • This is what we want the response to be. We want an authorization code, so we just use the value code.
• Prompt
  • This specifies whether or not to prompt the user to consent to the permissions. If we did not have this, and changed permissions, the request would just unexpectedly fail. Very frustrating. But it can be removed once permission has been granted as long as you don't change the permissions. If the application is accessing an API that requires admin permission, this value should be admin_consent.

Alright, so once we shoot off this request we will be redirected to the login page. We login, accept the permissions, and then we should be redirected to here: http://123AzureApiTutorial.com/code?code=SOME_REALLY_LONG_STRING_OF_CHARACTERS. That string of characters is the code.

Getting the Access Token

Next, we take the code and use it to get the access_token. To do so, we need to make another request.

(POST) https://login.microsoftonline.com/<tenant-id>/oauth2/token

In addition to the url, we need to add parameters. These should be consistent with the content type application/x-www-form-urlencoded. This means they are submitted as form parameters. They are as follows:

• client_id
  • This is again the client id (Application ID) we already have.
• client_secret
  • This is the Application Key we generated earlier. I hope you saved it! If not, go back to that step and generate another one.
• code
  • This is the value of the code we just received: SOME_REALLY_LONG_STRING_OF_CHARACTERS.
• `grant_type
  • Because we're going the authorization code route, this value should be authorization_code
• redirect_uri
  • This is the redirect uri we specified for the API Tutorial. The value from our example should be http://123AzureApiTutorial.com/code.
• resource
  • This is very important. It is the resource API we want to access. For the Azure API, this value is https://management.azure.com.

Our response will be a json object with a variety of fields. Of these, the one we care about is access_token. Yay!

Client Credentials

This methodology skips getting the code (and thus needing the redirect_uri) at the expense of not getting an id_token.

The request is the same as in the Getting the Access Token section, with a few small differences.

• We do not need to specify redirect_uri.
• The value of grant_type should change to client_credentials.

Alright, we have an access_token! Now we're cooking!

Making the API request

With all the prep work thus far, this is the easiest part of the process.

The API URL we are requesting against is:

https://management.azure.com/subscriptions/<subscription-id>/providers/Microsoft.Compute/virtualMachines?api-version=2016-03-30

Add the following header to the request:

Authorization: Bearer <access-token>. Yes, the access_token value must be prefaced with the word "Bearer" in the header value.

"But wait!" You exclaim. "How do I get the subscription id?"

Excellent question! To find it through the portal, click Subscriptions -> -> Overview and copy the Subscription Id value.

Use that value, and run the request. You should see all the vms listed!

Common errors thus far

InvalidAuthenticationToken

When making the API request, you get an error response that says something like this: InvalidAuthenticationToken: The access token is invalid. This means you haven't added the API permissions to the API Tutorial. Go back to the Add the correct permissions step and double-check you have the right permissions. Also, when requesting the token make sure you use the prompt=consent, otherwise the you will not be prompted with the new permissions and the token will fail.

InvalidAuthenticationTokenTenant

Make sure that the tenant-id used when requesting the token belongs to the subscriber used when making the API call.

Answer 2

First, we can find this rest API in azure resource portal. It is the same with Azure CLI command azure vm list.

I have tested it on my local with http request. here is my tested screenshot:

Request URL: https://management.azure.com/subscriptions/<subscription ID>/providers/Microsoft.Compute/virtualMachines?api-version=2016-03-30

Header:Authorization: bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI.....

So It is very import if we get the access token. The following demonstrate us how to get the access token.

Get Token(POST):

Request URL: https://login.microsoftonline.com/<tenant id>/oauth2/token

Body: grant_type=client_credentials&client_id=<client id>&resource=https%3A%2F%2Fmanagement.core.windows.net%2F&client_secret=<client secret>

Here is my screenshot in fildder:

We need to get client id and client secret in azure ad application. For how to regist an application in Azure AD. Please have a look at this article: https://learn.microsoft.com/en-us/azure/azure-resource-manager/resource-group-create-service-principal-portal.

Please note:

1) we need to add "Windows Azure Service Management API" in portal "Required permissions" like the following screenshot: 2) We need assign "Contributor" for this service principal. click subscription-> Access Control-> click Add -> click "Select a Role" -> click Contributor->click Add User-> Find the application you created above-> click OK.