[Feature] Ldap auth support

[simonhir]

Relevant component

refarch-gateway

Problem description (optional)

Currently only oAuth2 can be used for authentication in the gateway and JWT is used for authentication for services behind the gateway.

Desired solution

As some of the open source RefArch applications are interesting for reusing in other municipalities/companies and not everyone of them uses a Keycloak for authentication the possibility to do the authentication and authorization via LDAP should be introduced.
For the DAVe Project this usecase was already externally requested.
Things to think about:

• Authorization: Roles/permissions via ldap-groups?
• Authentication between Gateway and Services
• Easy maintanability
• The alternatives could be more practical

Indirectly might require it-at-m/refarch-templates#354 and it-at-m/refarch-templates#258 as prerequisite.

Considered alternatives (optional)

• Integrate LDAP into Keycloak: https://www.keycloak.org/docs/latest/server_admin/#adding-a-provider

Additional context (optional)

• DAVe Issue: LDAP dave-backend#80
• Internal tracking issue: https://git.muenchen.de/ccse/auftragsmanagement/einsaetze/-/issues/443

No duplicate

• I confirm that this issue is not a duplicate

Code of Conduct

• I agree to follow this project's Code of Conduct

[simonhir]

As the implementation should be done within it-at-m/dave-backend#80 this is blocked for now.