I wish to bring it your kind notice that Currently I am Integrating Salesforce to Box.com and I am facing an issue regarding uploading a file.

 I got the following error:

"Access to XMLHttpRequest at 'https://upload.box.com/api/2.0/files/content?parent_id=0' from origin 'https://c.ap15.visual.force.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource."

Let me know if You have any further queries on the same, awaiting your response.

Thanks