Add user_login to /helix/streams
Some users have display names (the "user_name" property) that do not work for IRC or even in URLs. This requires an additional call to /helix/users with the ID to get the login which I find more crucial than the display name that is already included.
Here are two examples:
The user "riotgames" (ID 36029255) has a display name with a space. "twitch.tv/Riot Games" does not redirect to "twitch.tv/riotgames".
The user "hanryang1125" (ID 103825127) has a display name with Korean characters. "twitch.tv/풍월량" does not redirect to "twitch.tv/hanryang1125".
Neither of these display name would work for IRC, which goes for most display names since channel capitalization is not allowed. Simply lowercasing the display name may work for most channels but would fail in those example cases.
As Alca mentioned, this has been completed and user name has been added to several API endpoint payloads. See the changelog for 2021-01-28. https://dev.twitch.tv/docs/change-log
This idea has been completed as of 2021‑01‑28.
Encountered this exact issue very recently. Annoying to have to do a separate API call with the user_id in order to get the login (and thus, the URL) for the user.