doas -- Prevent passing of environment variables

Jesse Smith (upstream author of the doas program) reported:

Previous versions of "doas" transferred most environment variables, such as USER, HOME, and PATH from the original user to the target user. Passing these variables could cause files in the wrong path or home directory to be read (or written to), which resulted in potential security problems.

Many thanks to Sander Bos for reporting this issue and explaining how it can be exploited.

[source]