startupplugin.html

<div id='myloginform'>
    <h1> some crazy login form styled to your website</h1>
    <form @click.prevent="onFormSubmit">
        <input v-model="nick" />
    </form>
</div>

<script>
export function run(kiwi, config) {
    var ctr = {
        template: '#myloginform',
        data: function() {
            return {
                nick: '',
                pass: '',
            };
        },
        methods: {
            startup: onFormSubmit(event) {
                // basically do this https://github.com/kiwiirc/kiwiirc/blob/master/src/components/startups/Welcome.vue#L277
            },
        },
    };
    kiwi.addStartup('myplugin', ctr);
    kiwi.state.settings.startupScreen = 'myplugin';

}
</script>