Currently the way you would do that is by using the short version in the custom field definition. This will be the programatic value that is persisted. For example:

US DE

Then in your message bundle (managed by the theme), you can translate those values into a more human readable option.

US=UNITED STATES DE=GERMANY

If we do not find a localized key, we will just use the key as the value which would then render as <option value="US">US</option>.

You are trying delete the field, instead of just removing it from a form. You cannot delete a field when a form is using it.

If you do not want a field displayed, you must remove it from a form.

Then, if you would like to delete the field definition you may.

If you have your own login form, you'll either be using the Login API or the OAuth Password grant. You will use one or the other, not both, each option will provide you roughly the same functionality. Totally up to you, the Login API is our own creation, the Password grant is defined by the OAuth RFC.

High level:

Collect email and password Call the Login API or the Token endpoint using the Password grant Collect the JSON response which will contain an access token (JWT)

Login API docs: https://fusionauth.io/docs/v1/tech/apis/login#authenticate-a-user

Password Grant: https://fusionauth.io/docs/v1/tech/oauth/endpoints#resource-owner-password-credentials-grant-request
https://fusionauth.io/docs/v1/tech/oauth/#example-resource-owner-password-credentials-grant