Bugfix RSA SecurID token decryption and PIN entry forms

Bugfix RSA SecurID token decryption and PIN entry forms

As of
https://gitlab.com/openconnect/openconnect/-/commit/386a6edb6d2d1d2cd3e9c9de8d85dc7bfda60d34,
all auth forms are required to have a non-NULL `auth_id`.

However, we forget to make stoken.c set the `auth_id` for the forms that it
creates for RSA SecurID token decryption and PIN entry.  Let's name these:

  - `_rsa_unlock`, for token decryption.
  - `_rsa_pin`, for PIN entry.  Also, rename the numeric PIN field to `pin`
    rather than `password`; there can't be any existing users relying on
    `--form-entry` to set its value, because that wouldn't work without the
    `auth_id`.

Fixes #388.

Signed-off-by: Daniel Lenski <dlenski@gmail.com>