esriConfig.defaults.io.alwaysUseProxy = true;
var myPortal = new esriPortal.Portal("http://www.arcgis.com");
Then, the Portal construction url is received by the proxy handler as:
And the decode form, retrieved with this:
string uri = context.Request.Url.Query.Substring(1);
Resolve uri to
Which should be:
For now I can work around it by don't set "alwaysUseProxy = true", and use "urlUtils.addProxyRule" instead., but is this a bug?