401 Error - Invalid Signature

401 Error - Invalid Signature

401 Error - Invalid Signature.png


Error Code Cause

Users will see this error when during the initial LMS configuration with VitalSource the LTI Secret was incorrectly entered, there are too many characters in the course name, or there is an Incorrectly formatted parameter context_title. 


Student / Faculty

  • Please reach out to your instructor and inform them of the error so they may reach out to the team that configured the link inside your institution's LMS. 
  • Use the link in the For More Help section below to submit a support request to VitalSource for assistance.  Would you please provide your School Name, LMS, Course, Section, Name of the Book you attempted to access, and a screenshot of the error?   

LMS Administrator

  • If the key/secret was incorrectly entered, re-enter the correct key and secret. 
  • In case of too many characters in the course name, reduce the number of characters on the course name. There is a character limit of 255 on the Course Title and Label.
  • If parameter context_title is incorrectly formatted, please advise the customer to correct the format and re-launch the eText. There are no special character requirements as long as they’re encoded correctly.
  • Double-check the launch  URL. If the launch URL ends with /books/, then that will throw an error.  This could happen in Canvas if they installed the tool with /books/ to make it simple to add a SKU at the prepopulated link later when adding to modules.  If they switch to course dash, they need to remove the ending slash.  

Moodle LMS Administrator

  • Moodle is prone to copy/paste errors with key/secrets that add whitespace before or after the actual text. Have the user paste into a product like Apple notes and verify that their notepad contains only the correct content. They can also click the view (eye) icon to check the first & last characters are not blanks.
  • Moodle also offers course managers the ability to configure a course-level tool rather than a global tool. At the initial setup of an LTI tool in Moodle (course), the user must decide where to place the Launch URL, and they are given two fields, "Tool URL"  and "Secure tool URL" the first one (non-secure) will cause Moodle to authenticate with Launch improperly. This can throw an invalid session key error or an invalid signature.
    • Move the Launch URL to the correct location to correct this.
  • Moodle can throw an Invalid Signature Error if either the activity name or the course title contains more than 72 characters. Reduce to fix.


For more help

To report this issue to VitalSource, please do the following:

  • Submit a request using the VitalSource Error Support Form.
  • In the error code drop down, enter the title of this Article.
  • Fill out all of the fields and include a copy of the error message you received. Please provide a screenshot of the error, the time stamp on the error code will help us troubleshoot the issue.

VitalSource Support will follow up with you after we resolve the issue or additional steps to troubleshoot.

Please note that reaching out to VitalSource Support outside of the webform may cause delays in resolving the error code.

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