OC Studio integration: Return address (`return.target`) doesn't work the first time

[snoesberger]

Describe the bug
The first time a user opens OC Studio from within the plugin, the return address parameter (return.target) in the Studio URL isn't correctly escaped. After they have finished the recording, the user is redirected to the wrong address, leading to a white browser window.
Once the user is authenticated for OC Studio and opens OC Studio again, the return address is correct.

The first time the OC Studio is opened, the Studio URL looks like this:
https://your-opencast.org/studio/index.html?upload.seriesId=12345678-1234-1234-1234-098765432109&upload.seriesField=hidden&upload.acl=%7B%22ROLE_IVT_OWNER_AAI_userid@my.org%22:[%22read%22,%22write%22],%22ROLE_AAI_USER_userid@my.org%22:[%22write%22,%22read%22,%22annotate%22,%22annotate-admin%22]%7D&return.target=https://my-ilias.org/ilias.php?baseClass=ilobjplugindispatchgui&cmdNode=qd:q5:19i&cmdClass=xoctEventGUI&cmd=index&ref_id=1234567&return.label=ILIAS

Once the user is authenticated and opens Studio again, the URL looks like this:
https://your-opencast.org/studio/index.html?upload.seriesId=12345678-1234-1234-1234-098765432109&upload.seriesField=hidden&upload.acl=%7B%22ROLE_IVT_OWNER_AAI_userid@my.org%22:[%22read%22,%22write%22],%22ROLE_AAI_USER_userid@my.org%22:[%22write%22,%22read%22,%22annotate%22,%22annotate-admin%22]%7D&return.target=https%3A%2F%2Fmy-ilias.org%2Filias.php%3FbaseClass%3Dilobjplugindispatchgui%26cmdNode%3Dqd%3Aq5%3A19i%26cmdClass%3DxoctEventGUI%26cmd%3Dindex%26ref_id%3D1234567&return.label=ILIAS

To Reproduce
Steps to reproduce the behavior:

1. User is logged-in in ILIAS but not in Opencast
2. Start OC Studio within a Opencast series in ILIAS
3. User is redirected to Shibboleth login page
4. User is logged in and starts OC Studio recording
5. Finish OC Studio recording and upload the recording
6. Click on the finish button -> "Exit and go back to ILIAS"
7. Browser opens a white page (https://your-ilias.org/ilias.php?baseClass=ilobjplugindispatchgui)

Expected behavior
Already the first, unauthorized time the user uses OC Studio, the return address should be correct.

Environment (please complete the following information):

• Plugin version: 8.3.2
• Opencast version 16

[dagraf]

In meeting: Possibly a problem in the configuration of UniBE's Opencast.