[FEATURE] Custom OIDC provider label & icon

[larsvik]

Description

When integrating Hemmelig with a custom OIDC provider (e.g., Keycloak), the login button currently displays the provider's technical name, such as "Keycloak." This label can be confusing for end-users, who may not know or care about the underlying authentication service.

Enhancements Requested:

1. Custom OIDC Provider Label:
   Allow administrators to define a custom display label for the OIDC provider login button. For example:

   Instead of "Login with Keycloak," show "Login using ID - Company".

2. Custom OIDC Provider Icon:
   Allow configuration of a custom icon for the OIDC login button (e.g., upload or reference an SVG/png).

3. UI-Only Native Login Disable:
   Add an option to completely hide the native (username/password) login form from the UI, but still allow access for admins or support via a query variable (e.g., /login?showLogin=true).
   This would reduce confusion/support requests from users who should always use SSO.

Use-case:
Many users are not familiar with terms like "Keycloak"; they only need to see "Login using ID – Company" with our logo. Also, fully disabling native login in the UI would ensure all users go through our SSO, while still providing a way for support or admin access if needed.

Current Behavior:

• OIDC provider name (e.g., "Keycloak") shown as is
• No icon customization
• No way to hide native login form

Requested Behavior:

• Option to set any label and icon for the OIDC login button
• Option to completely hide native login UI, enabled dynamically only if needed

Screenshots

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Additional information

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