How to draw a solid line, that fades out to one side in GIMP?

Question

How would you draw something like that blue border above, where there's a solid line that fades out to total transparency on one side, in GIMP?

Answer 1

I just noticed the little GIMP tag, a quick search enabled me to find this tutorial for creating an 'Inner Glow' type effect in GIMP

The layer style Inner Glow in Photoshop, and equivalents in other software, will do that for you:

Answer 2

I found a simple way to achieve my goal by downloading the Gimp plugin Layer Effects, which adds an inner glow effect, among others, like what I imagine Photoshop already has built-in.