Different providers have different requirements. I have an example of how to post messages to Twitter:

http://www.topwizprogramming.com/freecode_twitter.html

There are people have have been able to connect to the Azure file system and Quickbooks online.

What service do you need to work with and what do you want to do with it?

I got OAuth2 working for sending emails via Gmail, but I have to tell you it's somewhat flaky. Don't know whether that's my code or Gmail. So I'm not sure there'd be a value in posting my code (nor, I'm afraid, do I have time right now to separate it out well enough to do so).

I have started to use R2 and I get an OAuth token and tried to simply pass it in to the REST calls and it seems to work for me. These are internal calls to REST APIs that we have written. I am surprised it worked so easily (just be adding the setrequestheader). I didn't think this was going to be supported until R3. Call me a happy camper :)

For the new RESTClient I simply add a request header with the token and it works

RESTClient rest 
rest = create RESTClient 
rest.setrequestheader("Authorization", "Bearer " + is_token )
ll_rc = rest.Retrieve( dw_1, "https://xxxxx/List?Product=ASSESS")

To pass a PDF with other data to a REST call, I have done the following:

string ls_file, jsondata
blob lblob_pdf
int li_rc
Long ll_rc, ll_stat
httpclient http 

ls_file =  "C:\test.pdf"

JSONParser json 
json = create JSONParser 

ll_rc = f_file_to_blob(ls_file , ref lblob_pdf)  //Converts file to blob

jsondata = '{"Access":"A", "Archive":"N","Product":"ASSESS"}' // data I need to pass to REST API

http = create httpclient 
string ls_BOUNDARY

ls_BOUNDARY = "$$$Boundary$$$"   // use or build a string that is not part of the other content!

// build the content
blob lblob_data
lblob_data = blob ("--"  + ls_BOUNDARY + "~r~n" + &
                  'Content-Disposition: form-data; name="dockey"' + &
                  "~r~nContent-Type: " + "application/json;charset=UTF-8" + &
                  "~r~n~r~n" + jsondata + "~r~n", EncodingUTF8!)

lblob_data = lblob_data + blob ("--"  + ls_BOUNDARY + "~r~n" + &
                  'Content-Disposition: form-data; name="docfile"; filename="' + 'Test' + '"' + &
                  "~r~nContent-Type: " + "application/octet-stream" + "~r~n~r~n", EncodingUTF8!) + &
    lblob_pdf + blob ("~r~n--"  + ls_BOUNDARY + "--~r~n", EncodingUTF8!)

http.setrequestheader( "Content-Type", "multipart/form-data; boundary=" + ls_BOUNDARY)
http.setrequestheader("Authorization", "Bearer " + is_write_token )

li_rc = http.sendrequest( 'POST', 'https://api.systest.worksafebc.com/v1/Correspondence_int/Upload', lblob_data)
 
ll_stat =  http.GetResponseStatusCode()

MessageBox("Stat", String(ll_stat ))

anyone has dropbox example?

Thanks

Bruce has posted some code samples up on CodeXchange: https://community.appeon.com/index.php/codeexchange/powerbuilder/43-rest-demo-app-for-powerbuilder-2017-r2-and-r3-new-features#41

Also, he did a good tech article on this: https://community.appeon.com/index.php/articles-blogs/tutorials-articles/2-powerbuilder/204-oauth-new-feature-in-powerbuilder-2017-r3

I have code for OAuth2 to access MS Dynamics using a service account and Azure.  It was in my Elevate presentation but I can't find it posted anywhere.  I'll try to dig it up.