Pandora refuses to issue API keys to anyone but a handful of hardware manufacturers who got the keys when their API program was first introduced in 2008. When asked for policy clarification, they said that their label licenses preclude software-based integrations; those licenses apparently only permit audio playback via their web player, their Pandora-branded apps, and third-party hardware.
We’ve contacted them repeatedly over the years to see if they would make an exception (first for Sooloos, then for HP Connected Music, and finally for Roon), eventually escalating to their C-level executives, with no success. This has long been a source of frustration for us, and we hope that Pandora eventually opens up to third-party integrations once again.