Adding a metadata value with space at start causes Blob upload to fail with authentication error - MAC signature found in the HTTP request is not the same as any computed signature

When uploading a blob using a metadata value that has spaces at start (such as using code below):

// blobName is any valid blobname such as "sample.txt" and fileStream is some stream with some valid blob content (say text)
BlobClient blobClient = container.GetBlobClient(blobName);
var headers = new BlobHttpHeaders
                {
                    ContentType = "application/octet-stream"            
                };

var blobUploadOptions = new BlobUploadOptions
            {
                HttpHeaders = headers,
                Metadata = new Dictionary<string, string>({"keyname", "  value with space at start"});
            };

            await blobClient.UploadAsync(fileStream, blobUploadOptions);

the upload fails with error:

Status: 403 (Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature.)
		ErrorCode: AuthenticationFailed
		
		Additional Information:
AuthenticationErrorDetail: The MAC signature found in the HTTP request 'Q0NXCFOX0S/0KbIYEmwBdma1cf+42H420hxijpw43kg=' is not the same as any computed signature.

Using Azure.Storage.Blobs 12.8.3

We encountered this error because we were storing a user assigned file name in the blob metadata (the blob-name itself did not use the user assigned file name) and Mac users sometimes have spaces in the file name at the beginning.

[compgumby]

This bit me too setting the metadata through Azure.Storage.Blobs. Took FOREVER to figure out why… ended up being a trailing space in the value of one of my key/value properties. Hard to spot when you don’t know to look for it.

[ak37165]

Thank you for the suggestion. However, it’s worth noting that the Azure JavaScript SDK does not have this issue. We can set metadata values with spaces when uploading directly from the browser (using SAS tokens issued by the server).

For some of our scenarios the browser must upload to our server and then the server uploads to the Azure blob storage (using the .net SDK). Here the spaces cause an issue (maybe because the MAC computed by the sdk does not include the spaces while the server computed MAC does).