Grails login.gsp not present

Implement your own login page by adding a file in your app under grails-app/views/login/auth.gsp - this will take precedence over the one in the plugin.

You can use auth.gsp from the plugin as a starting point for yours. It can be found here: https://github.com/grails-plugins/grails-spring-security-core/blob/master/plugin/grails-app/views/login/auth.gsp

I'm not aware of any command that puts the views auth.gsp or denied.gsp in your app.

First, We need to add Spring Security Core Plugin as a dependency: /build.gradle

compile 'org.grails.plugins:spring-security-core:3.2.0.M1'

Then,

There are two ways to override auth.gsp. By creating manually Controller and gsp or by using spring-security-ui plugin.

I have used second way to generate custom login page:

First, We need to add Spring Security Core Plugin as a dependency: /build.gradle

compile 'org.grails.plugins:spring-security-core:3.2.0.M1'

Use s2-quickstart to generate the default Spring Security Core domain classes:

grails s2-quickstart demo User Role

s2-quickstart script generates three domain classes; User, Role and UserRole.

Then install Grails spring-security-ui plugin from here

use grails s2ui-override auth command to override the login/auth.gsp form (this will create the login form so that you override it). Note: This command will not create controller. It create view at path login/auth.gsp

Use grails s2ui-override layout to override the layouts for the form(this will create the springSecurityUI.gsp layout so that you override it)

References: enter link description here

Note: Please check plugin documentation as per your grails version.

Hope this will helps you.

Must I run another command to generate it (and the controller)?

No. You could if you wanted to but you could also write the files yourself if you prefer. If you want to generate them, the spring-security-ui plugin can help with that. See https://grails-plugins.github.io/grails-spring-security-ui/latest/index.html#customization for more info.