Issue while downloading blob document using account SAS with Azure Java SDK

Question

Hello ,

I am trying to download a blob file using account SAS .

I have written following method to generate SAS token

 public static String getAccountSAS(String accountName, String accountKey, String endpoint, String startTime,
 String endTime, String apiVersion) throws UnsupportedEncodingException {

String stringToSign = accountName + "\n" + "r\n" + "b\n" + "sco\n" + startTime + "\n" + endTime + "\n" + "\n"
            + "https\n" + apiVersion + "\n";

    String signature = getHMAC256(accountKey, stringToSign);

    String sasToken = "sv=" + apiVersion + "&ss=b" + "&srt=sco" + "&sp=r" + "&st="
            + URLEncoder.encode(startTime, "UTF-8") + "&se=" + URLEncoder.encode(endTime, "UTF-8") + "&spr=https"
            + "&sig=" + URLEncoder.encode(signature, "UTF-8");


    return sasToken;
 }

 private static String getHMAC256(String accountKey, String signStr) {
 String signature = null;
 try {
 SecretKeySpec secretKey = new SecretKeySpec(Base64.getDecoder().decode(accountKey), "HmacSHA256");
 Mac sha256HMAC = Mac.getInstance("HmacSHA256");
 sha256HMAC.init(secretKey);
 signature = Base64.getEncoder().encodeToString(sha256HMAC.doFinal(signStr.getBytes("UTF-8")));
 } catch (Exception e) {
 e.printStackTrace();
 }
 return signature;
 }

Allow below is the code to generate Blob Container client and download the file -

 String sasToken = getAccountSAS(mapString.get("accountName"), mapString.get("accessKey"),
 mapString.get("endpoint"), mapString.get("startTime"), mapString.get("endTime"),
 mapString.get("apiversion"));




  BlobServiceClient storageClient = new
   BlobServiceClientBuilder().endpoint(mapString.get("endpoint"))
   .sasToken(sasToken)
   .buildClient();

 BlobContainerClient blobContainerClient = storageClient.getBlobContainerClient("demo");

 blobContainerClient.listBlobs().forEach(blobItem -> {
 System.out.println("Item Name" + blobItem.getName());
 BlobClient blobClient = blobContainerClient.getBlobClient(blobItem.getName());
 blobClient.downloadToFile(
blobItem.getName().replace("/", "-"));

 });

But the program is giving following exception -

Exception in thread "main" com.azure.storage.blob.models.BlobStorageException: Status code 403, "<?xml version="1.0" encoding="utf-8"?><Error><Code>AuthenticationFailed</Code><Message>Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature.
RequestId:294f4e24-301e-004f-7203-980252000000
Time:2020-10-01T14:56:40.4833994Z</Message><AuthenticationErrorDetail>Signature fields not well formed.</AuthenticationErrorDetail></Error>"

I am using azure-store-blob v12.7.0

Thanks in advance.

Answer 1

@Pramit Bhaumik
Apologies for the delay in responding here. BlobServiceClient.generateAccountSas is available, which should make this much simpler for you. Please try using this built in method for generating the account SAS and see if that works for you.

Hope this helps! Let us know if you have any further questions or issues.

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