--- a/NEWS	Tue Apr 14 07:19:44 2026 +0200
+++ b/NEWS	Wed Apr 29 13:57:52 2026 +0200
@@ -2,6 +2,8 @@
 ===============================
 
 * Fix opening of viewers if Orthanc is not branched at the root of the server
+* Disabled libcurl "Expect: 100-continue" header during LTI registration,
+  which is not properly handled by certain Moodle deployments
 
 
 Version 1.1 (2025-11-07)

--- a/Sources/LTI/LTIRoutes.cpp	Tue Apr 14 07:19:44 2026 +0200
+++ b/Sources/LTI/LTIRoutes.cpp	Wed Apr 29 13:57:52 2026 +0200
@@ -544,10 +544,24 @@
 
   {
     OrthancPlugins::HttpClient client;
-    client.SetTimeout(5);  // 5 seconds to avoid freezing
+    client.SetTimeout(10);  // 10 seconds to avoid freezing
     client.SetMethod(OrthancPluginHttpMethod_Post);
     client.SetUrl(Orthanc::SerializationToolbox::ReadString(platform, "registration_endpoint"));
     client.AddHeader("Authorization", "Bearer " + token);
+    client.AddHeader("Content-Type", Orthanc::EnumerationToString(Orthanc::MimeType_Json));
+
+    /**
+     * By default, libcurl adds an "Expect: 100-continue" header to
+     * POST/PUT requests, expecting the server to acknowledge before
+     * the body is sent. While this is valid HTTP/1.1 behavior, some
+     * infrastructures (notably certain Moodle deployments) do not
+     * handle this handshake correctly, resulting in the request body
+     * being received as empty. Explicitly setting "Expect" to an
+     * empty string disables this mechanism and causes the body to be
+     * sent immediately together with the headers.
+     **/
+    client.AddHeader("Expect", "");
+
     client.SetBody(registration.toStyledString());
     OrthancPlugins::HttpHeaders headers;
     client.Execute(headers, response);