It looks like amazon's developer console has changed slightly (again). There is now a link in the "Security Profile Management" that says "Login with Amazon". Clicking this link will enable one of your security profiles to have the previously missing "Web Settings" tab.
It does ask for some new URL, a "Consent Privacy Notice URL" in addition to the "Return URL". I don't know if this privacy notice url really does anything other than displaying a privacy notice somewhere down the line, but filling it in with any seemingly random URL appears to make it happy.
After getting the "Web Settings" tab to show up, you do get a Client ID and Client Secret. Entering them into Stablebit CloudDrive and clicking "Connect" (on an already existing volume, I was trying to reattach) I get this error message from stablebit (in a web broswer, with the crying emoticon):
Controller: Redirect
Action: AmazonCloudDrive
Error: Sorry, but the provider did not send us a valid secret code so we can't continue.
System.Exception: Sorry, but the provider did not send us a valid secret code so we can't continue. at StableBitWeb.RedirectController.OAuth2Model.Validate() at StableBitWeb.RedirectController.AmazonCloudDrive(OAuth2Model Model) at lambda_method(Closure , ControllerBase , Object[] ) at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass42.b__41() at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass8`1.b__7(IAsyncResult _) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End() at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass37.<>c__DisplayClass39.b__33() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass4f.b__49() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass37.b__36(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End() at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass25.<>c__DisplayClass2a.b__20() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass25.b__22(IAsyncResult asyncResult)