You do not mention what versions of MediaWiki, PluggableAuth, and SimpleSAMLphp you are using.

I just tested with MediaWiki 1.32, PluggableAuth 5.7, and OpenID Connect 5.0, and it works as expected. The user is redirected to the page that was in the original link after authentication. I do not have a test environment set up with SimpleSAMLphp right now, so I cannot test if the same is true for SimpleSAMLphp. Perhaps @Osnard or @MarkAHershberger can comment on whether this works in their environments.

Hi Cindy,

sorry for the missing version information. We are using
MW 1.31.1
PluggableAuth 5.4
SimpleSAMLphp 4.4

Did you set

$wgPluggableAuth_EnableAutoLogin = true;

?

Yes, I did enable auto login.

Also, what version of the SimpleSAMLphp library are you using?

I did have a similar problem with SimpleSAMLphp in pre-MediaWiki 1.27, but the code is significantly different since the change in the core MediaWiki authentication framework in MediaWiki 1.27+. That rewrite fixed the problem I was having at that time. If I recall correctly, the problem never existed in OpenID Connect.

We are using simplesamlphp version 1.16.2.

I messed around with the code a little bit and found some kind of solution (meaning it works now as expected but I am not sure if it's a good idea to do it like this):
In extensions/PluggableAuth/includes/PluggableAuthHooks.php I added these two lines at the end of
function doBeforeInitialize (right after $out->redirect(
...
... );

$title = $oldTitle;
$out->output();

As I see it the problem is this: If I don't do this, the "$title" of the current http-request gets changed to Special:UserLogin which makes SpecialPageFactory::executePath() kick in which breaks the intended redirect (which is correctly stated in the comment on the first line of that function) as it does another redirect (without adding returnto and returntoquery parameters to it).

But as it works for you I am probably missing something...

Ah, I just noticed that you are using PluggableAuth version 5.4. This problem was fixed in version 5.6 with this patch: https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/PluggableAuth/+/08efbf2053b25b1efd8dc5208d40bf2a046ccdaf.