getting 403 forbidden webexception for azure blob put request - azure

Question

I am using this code to upload some text directly to azure blob using rest api. I am getting an webexception 403 forbidden. Can someone plaese tell me where am i going wrong in my code
private String CreateAuthorizationHeader(String canonicalizedString, CloudBlob blob)
{
String signature = string.Empty;
using (HMACSHA256 hmacSha256 = new HMACSHA256())
{
Byte[] dataToHmac = System.Text.Encoding.UTF8.GetBytes(canonicalizedString);
signature = Convert.ToBase64String(hmacSha256.ComputeHash(dataToHmac));
}
String authorizationHeader = String.Format(CultureInfo.InvariantCulture, "{0} {1}:{2}", "SharedKeyLite", myaccount, signature);
return authorizationHeader;
}
private void PutBlob(String containerName, String blobName , CloudBlob blob)
{
String requestMethod = "PUT";
String urlPath = String.Format("{0}", blobName);
String storageServiceVersion = "2009-10-01";
String dateInRfc1123Format = DateTime.UtcNow.ToString("R", CultureInfo.InvariantCulture);
// if (uploadPST.HasFile)
// {
string content = "Sample file";
// Stream content = uploadPST.FileBytes;
UTF8Encoding utf8Encoding = new UTF8Encoding();
Byte[] blobContent = utf8Encoding.GetBytes(content);
Int32 blobLength = blobContent.Length;
const String blobType = "BlockBlob";
/* String canonicalizedHeaders = String.Format(
"x-ms-blob-type:{0}\nx-ms-date:{1}\nx-ms-version:{2}",
blobType,
dateInRfc1123Format,
storageServiceVersion);*/
String canonicalizedHeaders = String.Format(
"x-ms-date:{0}\nx-ms-meta-m1:{1}\nx-ms-meta-m1:{2}",
dateInRfc1123Format,
"v1",
"v2");
String canonicalizedResource = String.Format("/{0}/{1}", myaccount, urlPath);
String stringToSign = String.Format(
"{0}\n\n{1}\n\n{2}\n{3}",
requestMethod,
"text/plain; charset=UTF-8",
canonicalizedHeaders,
canonicalizedResource);
String authorizationHeader = CreateAuthorizationHeader(stringToSign, blob);
Uri uri = new Uri(CloudStorageAccount.FromConfigurationSetting("DataConnectionString").BlobEndpoint + "/" + urlPath);
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
request.Method = requestMethod;
// request.Headers.Add("x-ms-blob-type", blobType);
request.Headers.Add("x-ms-date", dateInRfc1123Format);
// request.Headers.Add("x-ms-version", storageServiceVersion);
request.Headers.Add("Authorization", authorizationHeader);
request.ContentLength = blobLength;
using (Stream requestStream = request.GetRequestStream())
{
requestStream.Write(blobContent ,0 ,blobLength);
}
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
String ETag = response.Headers["ETag"];
}
// }
}

Answer 1

First, you construct an HMACSHA256 object using the default constructor -- this causes a random key to be generated and used for signing. What you want is the overload which accepts a string - and pass the azure account key.
Still, signing the request 'manually' can be tricky, as there are a lot of things to do and it's easy to mess up or forget something. Instead, I recommend you use the SignRequest method of StorageCredentialsAccountAndKey class (msdn doc) For instance;
// ...there exists a request object, and strings for the account name and key
var creds = new StorageCredentialsAccountAndKey(accountName, accountKey);
creds.SignRequest(request);
This will do everything needed to sign the request properly, including creating a canonicalized headers string, creating a date with the correct format, etc.