[Microsoft身份平台]Microsoft身份平台和OAuth 2.0客户端凭据流

The OAuth 2.0 client credentials grant flow permits a web service (confidential client) to use its own credentials, instead of impersonating a user, to authenticate when calling another web service. The grant specified in RFC 6749, sometimes called two-legged OAuth, can be used to access web-hosted resources by using the identity of an application. This type is commonly used for server-to-server interactions that must run in the background, without immediate interaction with a user, and is often referred to as daemons or service accounts.

In the client credentials flow, permissions are granted directly to the application itself by an administrator. When the app presents a token to a resource, the resource enforces that the app itself has authorization to perform an action since there is no user involved in the authentication. This article covers both the steps needed to:

• Authorize an application to call an API
• How to get the tokens needed to call that API.

This article describes how to program directly against the protocol in your application. When possible, we recommend you use the supported Microsoft Authentication Libraries (MSAL) instead to acquire tokens and call secured web APIs. You can also refer to the sample apps that use MSAL. As a side note, refresh tokens will never be granted with this flow as client_id and client_secret (which would be required to obtain a refresh token) can be used to obtain an access token instead.

For a higher level of assurance, the Microsoft identity platform also allows the calling service to authenticate using a certificate or federated credential instead of a shared secret. Because the application's own credentials are being used, these credentials must be kept safe. Never publish that credential in your source code, embed it in web pages, or use it in a widely distributed native application.

The entire client credentials flow looks similar to the following diagram. We describe each of the steps later in this article.

An app typically receives direct authorization to access a resource in one of two ways:

• Through an access control list (ACL) at the resource
• Through application permission assignment in Microsoft Entra ID

These two methods are the most common in Microsoft Entra ID and we recommend them for clients and resources that perform the client credentials flow. A resource can also choose to authorize its clients in other ways. Each resource server can choose the method that makes the most sense for its application.

A resource provider might enforce an authorization check based on a list of application (client) IDs that it knows and grants a specific level of access to. When the resource receives a token from the Microsoft identity platform, it can decode the token and extract the client's application ID from the appid and iss claims. Then it compares the application against an access control list (ACL) that it maintains. The ACL's granularity and method might vary substantially between resources.

A common use case is to use an ACL to run tests for a web application or for a web API. The web API might grant only a subset of full permissions to a specific client. To run end-to-end tests on the API, you can create a test client that acquires tokens from the Microsoft identity platform and then sends them to the API. The API then checks the ACL for the test client's application ID for full access to the API's entire functionality. If you use this kind of ACL, be sure to validate not only the caller's appid value but also validate that the iss value of the token is trusted.

This type of authorization is common for daemons and service accounts that need to access data owned by consumer users who have personal Microsoft accounts. For data owned by organizations, we recommend that you get the necessary authorization through application permissions.

In order to enable this ACL-based authorization pattern, Microsoft Entra ID doesn't require that applications be authorized to get tokens for another application. Thus, app-only tokens can be issued without a roles claim. Applications that expose APIs must implement permission checks in order to accept tokens.

If you'd like to prevent applications from getting role-less app-only access tokens for your application, ensure that assignment requirements are enabled for your app. This will block users and applications without assigned roles from being able to get a token for this application.

Instead of using ACLs, you can use APIs to expose a set of application permissions. These are granted to an application by an organization's administrator, and can be used only to access data owned by that organization and its employees. For example, Microsoft Graph exposes several application permissions to do the following:

• Read mail in all mailboxes
• Read and write mail in all mailboxes
• Send mail as any user
• Read directory data

To use app roles (application permissions) with your own API (as opposed to Microsoft Graph), you must first expose the app roles in the API's app registration in the Microsoft Entra admin center. Then, configure the required app roles by selecting those permissions in your client application's app registration. If you haven't exposed any app roles in your API's app registration, you won't be able to specify application permissions to that API in your client application's app registration in the Microsoft Entra admin center.

When authenticating as an application (as opposed to with a user), you can't use delegated permissions because there is no user for your app to act on behalf of. You must use application permissions, also known as app roles, that are granted by an admin or by the API's owner.

For more information about application permissions, see Permissions and consent.

Typically, when you build an application that uses application permissions, the app requires a page or view on which the admin approves the app's permissions. This page can be part of the app's sign-in flow, part of the app's settings, or a dedicated connect flow. It often makes sense for the app to show this connect view only after a user has signed in with a work or school Microsoft account.

If you sign the user into your app, you can identify the organization to which the user belongs to before you ask the user to approve the application permissions. Although not strictly necessary, it can help you create a more intuitive experience for your users. To sign the user in, follow the Microsoft identity platform protocol tutorials.

When you're ready to request permissions from the organization's admin, you can redirect the user to the Microsoft identity platform admin consent endpoint.

// Line breaks are for legibility only.

GET https://login.microsoftonline.com/{tenant}/adminconsent?
client_id=00001111-aaaa-2222-bbbb-3333cccc4444
&state=12345
&redirect_uri=http://localhost/myapp/permissions

Pro tip: Try pasting the following request in a browser.

https://login.microsoftonline.com/common/adminconsent?client_id=00001111-aaaa-2222-bbbb-3333cccc4444
&state=12345&redirect_uri=http://localhost/myapp/permissions

At this point, Microsoft Entra ID enforces that only a tenant administrator can sign in to complete the request. The administrator will be asked to approve all the direct application permissions that you have requested for your app in the app registration portal.

If the admin approves the permissions for your application, the successful response looks like this:

GET http://localhost/myapp/permissions?tenant=aaaabbbb-0000-cccc-1111-dddd2222eeee&state=state=12345&admin_consent=True

If the admin does not approve the permissions for your application, the failed response looks like this:

GET http://localhost/myapp/permissions?error=permission_denied&error_description=The+admin+canceled+the+request

After you've received a successful response from the app provisioning endpoint, your app has gained the direct application permissions that it requested. Now you can request a token for the resource that you want.

After you've acquired the necessary authorization for your application, proceed with acquiring access tokens for APIs. To get a token by using the client credentials grant, send a POST request to the /token Microsoft identity platform. There are a few different cases:

• Access token request with a shared secret
• Access token request with a certificate
• Access token request with a federated credential

POST /{tenant}/oauth2/v2.0/token HTTP/1.1           //Line breaks for clarity
Host: login.microsoftonline.com:443
Content-Type: application/x-www-form-urlencoded

client_id=00001111-aaaa-2222-bbbb-3333cccc4444
&scope=https%3A%2F%2Fgraph.microsoft.com%2F.default
&client_secret=qWgdYAmab0YSkuL1qKv5bPX
&grant_type=client_credentials

# Replace {tenant} with your tenant!
curl -X POST -H "Content-Type: application/x-www-form-urlencoded" 
-d 'client_id=00001111-aaaa-2222-bbbb-3333cccc4444
&scope=https%3A%2F%2Fgraph.microsoft.com%2F.default&client_secret=A1bC2dE3f...
&grant_type=client_credentials' 
'https://login.microsoftonline.com/{tenant}/oauth2/v2.0/token'

POST /{tenant}/oauth2/v2.0/token HTTP/1.1               // Line breaks for clarity
Host: login.microsoftonline.com:443
Content-Type: application/x-www-form-urlencoded

scope=https%3A%2F%2Fgraph.microsoft.com%2F.default
&client_id=11112222-bbbb-3333-cccc-4444dddd5555
&client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiIsIng1dCI6Imd4OHRHeXN5amNScUtqRlBuZDdSRnd2d1pJMCJ9.eyJ{a lot of characters here}M8U3bSUKKJDEg
&grant_type=client_credentials

The parameters for the certificate-based request differ in only one way from the shared secret-based request: the client_secret parameter is replaced by the client_assertion_type and client_assertion parameters.

POST /{tenant}/oauth2/v2.0/token HTTP/1.1               // Line breaks for clarity
Host: login.microsoftonline.com:443
Content-Type: application/x-www-form-urlencoded

scope=https%3A%2F%2Fgraph.microsoft.com%2F.default
&client_id=11112222-bbbb-3333-cccc-4444dddd5555&client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiIsIng1dCI6Imd4OHRHeXN5amNScUtqRlBuZDdSRnd2d1pJMCJ9.eyJ{a lot of characters here}M8U3bSUKKJDEg
&grant_type=client_credentials

Everything in the request is the same as the certificate-based flow, with the crucial exception of the source of the client_assertion. In this flow, your application does not create the JWT assertion itself. Instead, your app uses a JWT created by another identity provider. This is called workload identity federation, where your apps identity in another identity platform is used to acquire tokens inside the Microsoft identity platform. This is best suited for cross-cloud scenarios, such as hosting your compute outside Azure but accessing APIs protected by Microsoft identity platform. For information about the required format of JWTs created by other identity providers, read about the assertion format.

A successful response from any method looks like this:

{
  "token_type": "Bearer",
  "expires_in": 3599,
  "access_token": "eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsIng1dCI6Ik1uQ19WWmNBVGZNNXBP..."
}

An error response (400 Bad Request) looks like this:

{
  "error": "invalid_scope",
  "error_description": "AADSTS70011: The provided value for the input parameter 'scope' is not valid. 
  The scope https://foo.microsoft.com/.default is not valid.
  \r\nTrace ID: 0000aaaa-11bb-cccc-dd22-eeeeee333333\r\nCorrelation ID: aaaa0000-bb11-2222-33cc-444444dddddd\r\n
  Timestamp: 2016-01-09 02:02:12Z",
  "error_codes": [
    70011
  ],
  "timestamp": "YYYY-MM-DD HH:MM:SSZ",
  "trace_id": "0000aaaa-11bb-cccc-dd22-eeeeee333333",
  "correlation_id": "aaaa0000-bb11-2222-33cc-444444dddddd"
}

Now that you've acquired a token, use the token to make requests to the resource. When the token expires, repeat the request to the /token endpoint to acquire a fresh access token.

GET /v1.0/users HTTP/1.1
Host: graph.microsoft.com:443
Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbG...

Try the following command in your terminal, ensuring to replace the token with your own.

curl -X GET -H "Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbG..." 'https://graph.microsoft.com/v1.0/users'

Read the client credentials overview documentation from the Microsoft Authentication Library