I need to add some codes to allow this code below here to send the photo over to facebook from Salesforce.
But I realize I keep on having bad request when I'm trying attach photos from Salesforce but if i use any photo from google the photo will be uploaded.
So I was thinking of adding in SSO for this program so that it can sign in and access the file.
Can help me the programming codes for HTTP POST SSO as I'm not familiar with SSO.

My Codes are in the image below:

I need a programming code for a custom button to help me transfer a specific file from Salesforce onto another website like dropbox for example.

Is it even possible?
If it is possible can show me a workable code?

If not are there any way around it?