Intermittent error AuthorizationHeaderMalformed when requesting for presigned url for viewing the file

Posted on April 15, 2024

I’m generating a pre-signed-URL using the AWSSDK.S3 nuget from a .Net app using the code below.

var s3Client = new AmazonS3Client(<accessKeyId>, <secreAccessKey>, new AmazonS3Config
{
    ServiceURL = <spacesEndpoint>
_});

var request = new GetPreSignedUrlRequest
{
    BucketName = <bucketName>,
    Key = <filePathKey>,
    Expires = DateTime.UtcNow.AddMinutes(10),
    ResponseHeaderOverrides = new ResponseHeaderOverrides
    {
        ContentDisposition = $"filename=\"{fileName}\"",
        ContentType = <contentType>
    }};

return _s3Client.GetPreSignedURL(request)

It works intermittently. In some cases, the generated URL is working and sometimes I get the error

<Error><Code>AuthorizationHeaderMalformed</Code><Message>The authorization header is malformed.</Message><Resource><do-space-file-path></Resource><RequestId>not available</RequestId></Error>

Has anyone encountered this before? Thanks!

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Bobby

April 15, 2024

Hi there,

Indeed, as this is intermittent it can be quite tricky to troubleshoot. So what I could suggest here is:

If possible, configure your .NET app to generate detailed logs of the pre-signed URL generation process, including timestamps, headers, and the calculated signature. This can help pinpoint discrepancies.
Try to compare the working and failing requests. When you get a working URL and a failing URL, carefully compare their structures. Look for small differences in encoding, headers, or timestamps.
Try generating a pre-signed URL for the same object using the AWS CLI or another client. If this works, it can help eliminate bucket permission or endpoint configuration issues: