If instructors or students encounter the error message "API Login Failed 'Oauth_signature' incorrect credentials and/or signature calculation" when accessing a Turnitin LTI assignment, it generally indicates a communication breakdown between the Learning Management System (LMS) and Turnitin.
Essentially, the digital signature sent by the LMS didn't match what Turnitin expected. This is usually caused by one of two things: hidden formatting in a user profile or conflicting configuration settings.
For Students: Check for "Invisible" Formatting
While this error often looks like a system-wide failure, it can happen to a single student if their profile data contains hidden characters (like line breaks or HTML) often introduced by copying and pasting names into the LMS.
The Cause: If a name was pasted into a profile, it may contain a hidden "line break" code (e.g.,
%0D%0A). Turnitin’s security check sees this extra code and rejects the login attempt.The Fix: You cannot fix this yourself. Please contact your Instructor to request that this is raised with your LMS Administrator.
Administrator Action:
Locate the student’s profile in the LMS
Completely delete the text in the First Name and Last Name fields
Manually type the names back in (do not use copy/paste)
Save the profile and ask the student to try the assignment again
For Instructors & Administrators: Resolve Configuration Conflicts
If multiple users (or just the instructor) are seeing this error, the issue is likely rooted in how the Turnitin LTI app is set up within your institution's LMS.
1. Duplicate External Apps
The most common cause is having the Turnitin LTI app configured more than once. If there are multiple versions of the Turnitin tool active in the "External Apps" settings, the system may use the wrong credentials to sign the request.
The Cause: Multiple configuratons of the Turnitin LTI app.
The Fix: An LMS Administrator should review the Account-level settings and remove any duplicate or outdated Turnitin LTI configurations.
2. Course-Level vs. Account-Level Conflicts
If your institution has already configured Turnitin at the Account (Global) level, instructors should not attempt to manually configure the app again within an individual Course level.
The Cause: A course-level configuration creates a "signature conflict" with the global settings.
The Fix: If you have manually added Turnitin as an app within your specific course settings, please delete that local configuration. The global, administrator-managed version is all you need to create assignments.
Summary Table: Which fix do I need?
| Who is seeing the error? | Likely Cause | Primary Solution |
|---|---|---|
A single student | Hidden characters in their LMS profile | Admin must re-type the student's name manually |
The instructor only | Course-level configuration conflict | Remove Turnitin from the "Course" settings |
Multiple users or Entire class | Duplicate LTI apps or Global setup error | Admin must remove duplicate apps at the Account level |