Couldn't you set

{% if url == "intranet.net" %}
 {% set pass = "password" %}
{% endif %}

<input type="password" value="{{ pass|default('') }} name="password" />

Couldn't you set the password to a variable on the login page if it is the correct intranet url?

{% if craft.request.getUrl() == "intranet.net" %}
 {% set pass = "password" %}
{% endif %}

<input type="password" value="{{ pass|default('') }} name="password" />