For specific location:

locations:
  foo:
    # ...
    options:
      all:
        insecure-no-password: true

Globally:

global:
  all:
    insecure-no-password: true

Note:

It's correct that restic is calling this parameter "insecure". In my use case, the backend is already encrypted (ZFS dataset) and I'm personally comfortable with not having additional encryption on the restic repo.

Most users shouldn't use "--insecure-no-password".