WeBWorK Main Forum

LTI error from Blackboard

by Michael Shulman -
Number of replies: 6
I have a problem with users logging into WeBWorK from Blackboard using the LTI module. It only seems to happen if a nontrivial amount of text is entered into the "Description" field when creating the Web Link content item from Blackboard that points to WeBWorK; if I leave the Description field empty then everything seems to work fine. The error messages are

Net::OAuth warning: your OAuth message appears to contain some multi-byte characters that need to be decoded via Encode.pm or a PerlIO layer first. This may result in an incorrect signature. at /usr/share/perl5/vendor_perl/Net/OAuth/Message.pm line 106. Net::OAuth warning: your OAuth message appears to contain some multi-byte characters that need to be decoded via Encode.pm or a PerlIO layer first. This may result in an incorrect signature. at /usr/share/perl5/vendor_perl/Net/OAuth/Message.pm line 106. OAuth verification failed. Check the Consumer Secret and that the URL in the LMS exactly matches the WeBWorK URL as defined in site.conf. E.G. Check that if you have https in the LMS url then you have https in \$server_root_url in site.conf at /opt/webwork/webwork2/lib/WeBWorK/Authen/LTIAdvanced.pm line 401.
The Net::OAuth warnings refer to multi-byte characters, and I notice that the debug_lti_parameters output includes:

resource_link_description => WeBWorK is our online homework system.Â You will always be able to access it from this link.Â TheÂ first time you go to WeBWorK, you must access it through this link.
which does indeed have some weird characters. (I didn't put them there; they must have been added by Blackboard for some reason.) Maybe some extra encoding needs to happen at some point?

Re: LTI error from Blackboard

by Danny Glin -
Was the text typed directly into Blackboard, or was it copied and pasted from some other source?  I've had experiences where pasting text also pasted additional characters which weren't necessarily visible.

Re: LTI error from Blackboard

by Michael Shulman -
It was typed directly in. But in any case, nothing in the Description box should cause the LTI authentication to fail, should it?

Re: LTI error from Blackboard

by Michael Gage -
I've experienced this error.  It's clearly a bug, but I just worked around it by not entering a description.

from a conversation I had with Alistair Kwan three years ago (read from bottom up):

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from Alistair:

Tighter hypothesis: if the web link is the first item in the folder, and the description field contains a newline, then it'll fail.

On Sep 7, 2013, at Sep 7 9:46 AM, Michael Gage wrote:

Interesting. :-). But at least we can work around it.

On Sep 6, 2013, at 11:37 PM, Alistair Kwan <alistair.kwan@rochester.edu> wrote:

Yes, you're right, Mike's with a very short text worked.

I should try it with texts of varying lengths to see if there's some invisible limit there — my text was maybe 300 chars long.

This was on production.

On Sep 6, 2013, at Sep 6 7:58 PM, Michael Gage wrote:

I thought one of my links had some text in the description field and it still worked.  But I can't be sure.

-----Original Message-----

From: Alistair Kwan [mailto:alistair.kwan@rochester.edu

Sent: Friday, September 06, 2013 7:28 PM

Cc: Gage, Michael; Brown, Lisa

Subject: Re: linking BB to hosted2 course

I just discovered something: if you enter text in the description field on the BB end, the link fails.  Empty the description field, and it works again!

Black magic...

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So the LTI link in Blackboard is apparently still flaky.  Aside from the annoyance of not being able to use the description field the LTI link worked for me all semester.

-- Mike