Apache proxy to images on s3 bucket stopped working

I’m using an s3 bucket to serve images for my wordpress site. Instead of having to change all the image urls to the s3 bucket, I set up a proxy from the main domain over to s3. I had this working before, but a couple weeks ago it suddenly stopped.

I set up s3 bucket to use a subdomain so I don’t have the long ugly default s3 url.

Here is what I have in the .htaccess file

# Rewrite uploads folder to the s3 bucket
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteRule ^/?wp-content/uploads(.*) http://content.site.com/wp-content/uploads$1 [P]
</IfModule>
#End S3 rewrite

Doing this it returns a 400 bad request with the following xml (Specific keys have been removed).

<Error>
<Code>InvalidArgument</Code>
<Message>Unsupported Authorization Type</Message>
<ArgumentName>Authorization</ArgumentName>
<ArgumentValue>Basic xxxxxxxxxxxxxxxxxxxxx</ArgumentValue>
<RequestId>xxxxxxxxxxxxxxxxxxxxxxxxxxxx</RequestId>
<HostId>
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
</HostId>
</Error>

Any suggestions as to why the error is happening would be greatly appreciated!