Add JWT based authentication and role-based access control

[blushi]

Prerequisites:

The user-api has currently no authentication/authorization implemented.

The tools to implement that are already there:

• JWT based authentication
• Role-based access control
• Secure password
• IAM service using the previous tools

Regarding the models, there are already:

• role with 4 predefined roles
• tenant
• user model already has auth related fields: Password, Token, RoleId, TenantId, LastLogin and LastPasswordChange but they need to be added to user protobuf.

TODOs:

1. Within services, the Server struct need to have additional data fields: an RBACService, a Securer and an AuthService:

   type AuthService interface {
   GetUser(context.Context) *model.AuthUser
   }

   Requests authorization need to be implemented in there. Please contact @blushi to discuss specifications.

Some inspiration from the Twisk project.

2. Database migration:

   • Add Role and Tenant tables
   • Insert default roles and tenant(s)

3. Adapt cmd/api/main.go

4. Don't forget about tests!