Object Storage Service:Authorize access

Background information

When you use the STS authentication mode or self-signed mode, make sure that the callback function that you implement can return the security token and signature. If you must obtain the token and signature from the app server by sending a request in the callback function, we recommend that you call the synchronous API operations included in the network library. The callback function runs in the child thread of the request generated by the SDK and does not block the main thread.

STS authentication mode

You can use Alibaba Cloud STS to authorize temporary access to OSS. STS is a web service that provides temporary access tokens for users. You can use STS to grant temporary access credentials that have a custom validity period and custom permissions to a third-party application or a RAM user that is managed by you. For more information about STS, see What is STS?

STS provides the following benefits:

• You need to only generate an access token and send the access token to a third-party application. You do not need to expose your AccessKey pair to the third-party application. You can specify the access permissions and the validity period of the token.
• The token automatically expires after the validity period. Therefore, you do not need to manually revoke the access permissions of a token.

To access OSS by using temporary access credentials provided by STS, perform the following operations:

1. Obtain temporary access credentials.

   The temporary access credentials consist of an AccessKey pair and a security token. The AccessKey pair consists of an AccessKey ID and an AccessKey secret. The minimum validity period of temporary access credentials is 900 seconds. The maximum validity period of temporary access credentials is the maximum session duration specified for the current role. For more information, see Specify the maximum session duration for a RAM role.

   You can use one of the following methods to obtain temporary access credentials:

   • Call the AssumeRole operation.

     For more information, see AssumeRole.

   • Use STS SDKs.

     For more information, see STS SDK overview.

2. Use temporary access credentials to initialize the SDK

   String endpoint = "http://oss-cn-hangzhou.aliyuncs.com";
   
   OSSCredentialProvider credentialProvider = new OSSStsTokenCredentialProvider("StsToken.AccessKeyId", "StsToken.SecretKeyId", "StsToken.SecurityToken");
   
   OSS oss = new OSSClient(getApplicationContext(), endpoint, credentialProvider);                  

   When you initialize the SDK by using temporary access credentials, take note of the validity period of an STS token.

   The following code provides an example on how to determine the validity period of an STS token:

   SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
   sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
   Date date = sdf.parse("<StsToken.Expiration>");
   long expiration = date.getTime() / 1000;
   // The STS token is about to expire within less than five minutes. 
   if (DateUtil.getFixedSkewedTimeMillis() / 1000 > expiration - 5 * 60) {
       oss.updateCredentialProvider(new OSSStsTokenCredentialProvider("StsToken.AccessKeyId", "StsToken.SecretKeyId", "StsToken.SecurityToken"));
   }

   • Manually update the STS token

     When the STS token is about to expire, you can create another OSSClient instance or update CredentialProvider by running the following command:

     oss.updateCredentialProvider(new OSSStsTokenCredentialProvider("StsToken.AccessKeyId", "StsToken.SecretKeyId", "StsToken.SecurityToken"));                   

   • Automatically update the STS token

     If you want the SDK to automatically update the STS token, you must implement callback in your app. The app uses the callback to obtain a federation token (STS token) and returns the token to the SDK. The SDK uses the STS token to generate signatures. When the STS token needs to be updated, the SDK calls the callback to obtain a new token.

     String endpoint = "http://oss-cn-hangzhou.aliyuncs.com";
     
     OSSCredentialProvider credentialProvider = new OSSFederationCredentialProvider() {
     
         @Override
         public OSSFederationToken getFederationToken() {
         // Obtain a federation token, construct the token, and then return the token as an OSSFederationToken object. If no federation token is obtained, null is returned. 
     
             OSSFederationToken token;
             // Obtain a federation token from your server. 
             return token;
         }
     };
     
     OSS oss = new OSSClient(getApplicationContext(), endpoint, credentialProvider);                    

     Note If you obtain all fields required to generate a token in other ways, you can also return these fields by using the callback. In this case, you must manually update the token, and then reconfigure OSSCredentialProvider of the OSSClient instance.

     If the URL of the server from which you request a token is http://localhost:8080/distribute-token.json, the following data is returned:

     {
         "StatusCode": 200,
         "AccessKeyId":"STS.iA645eTOXEqP3cg3****",
         "AccessKeySecret":"rV3VQrpFQ4BsyHSAvi5NVLpPIVffDJv4LojU****",
         "Expiration":"2015-11-03T09:52:59Z",
         "SecurityToken":"CAES7QIIARKAAZPlqaN9ILiQZPS+JDkS/GSZN45RLx4YS/p3OgaUC+oJl3XSlbJ7StKpQ****"}                    

     The following code provides an example on how to implement OSSFederationCredentialProvider:

     OSSCredentialProvider credetialProvider = new OSSFederationCredentialProvider() {
         @Override
         public OSSFederationToken getFederationToken() {
             try {
                 URL stsUrl = new URL("http://localhost:8080/distribute-token.json");
                 HttpURLConnection conn = (HttpURLConnection) stsUrl.openConnection();
                 InputStream input = conn.getInputStream();
                 String jsonText = IOUtils.readStreamAsString(input, OSSConstants.DEFAULT_CHARSET_NAME);
                 JSONObject jsonObjs = new JSONObject(jsonText);
                 String ak = jsonObjs.getString("AccessKeyId");
                 String sk = jsonObjs.getString("AccessKeySecret");
                 String token = jsonObjs.getString("SecurityToken");
                 String expiration = jsonObjs.getString("Expiration");
                 return new OSSFederationToken(ak, sk, token, expiration);
             } catch (Exception e) {
                 e.printStackTrace();
             }
             return null;
         }
     };                    

Self-signed mode

Signed URLs

You can generate a signed URL and provide the URL to a visitor for temporary access. When you generate a signed URL, you can specify the validity period of the URL to limit the period of time during which the visitor can access the object.

The following code provides an example on how to generate a signed URL and use the signed URL to upload and download objects.