Group Attendance Reminder Linking to Page That Requires Authentication

[arranf]

This is reproducible on my production installation, I've created a community troubleshooting request to find if others have run into similar difficulty because I realised I couldn't replicate this on the demo install because Mandrill/SMTP weren't setup.

Steps to Reproduce:

1. Create a Group Type that takes attendance and has leaders with edit/view/etc.
2. Create group with schedule and a leader
3. Set Group Attendance Email job to send out emails for the new group type

What I Expect:
A click-through no login link to input attendance for a particular week

What Actually Happens:
The link takes you to the correct page but the following messages appears
"Sorry
You're not authorized to update the attendance for the selected group."

Logging in allows you to input the attendance