I recommend upgrading to 2.19 (although it is still in the release candidate phase, and not officially released). There are nice features for LTI in the upcoming release. There are updated instructions on how to set things up for 2.18 and 2.19 at https://webwork.maa.org/wiki/LTI_Authentication_(for_WeBWorK_2.18_or_newer). The instructions also include details on how to set things up for the new features for 2.19.
WeBWorK Main Forum
Who is using LTI to connect WeBWorK to an LMS?
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