Fix BFLA (Broken Function Level Authorization) in Roda

BFLA (Broken Function Level Authorization) is a critical vulnerability where an application fails to verify if a user has the appropriate privileges to access a specific function. In Roda's routing tree, developers often mistake authentication for authorization. Just because a user is logged in doesn't mean they should be hitting administrative branches. To secure a Roda app, you must implement granular access control checks at every sensitive route branch.

The Vulnerable Pattern

class App < Roda
  route do |r|
    r.on "api" do
      # Assume user is authenticated via middleware
      r.on "users" do
        r.get do
          # Any authenticated user can list all users
          User.all.to_json
        end
    # VULNERABLE: No check to see if current_user is an admin
    r.post "delete", Integer do |id|
      User[id].destroy
      { status: 'success' }.to_json
    end
  end
end
end
end

The Secure Implementation

The vulnerability exists because the routing logic assumes that being inside the 'api' branch is sufficient protection. To fix this, you must implement a 'Guard Clause' pattern. Before executing sensitive logic (the leaf of the route), verify the user's role or permissions. Using `r.halt` in Roda is the standard way to terminate the request immediately and return a 403 Forbidden status if the authorization check fails. For larger applications, consider using a dedicated authorization plugin or a policy-based approach like Pundit to keep the routing tree clean.

class App < Roda
  route do |r|
    r.on "api" do
      r.on "users" do
        r.get do
          User.all.to_json
        end
    r.post "delete", Integer do |id|
      # SECURE: Explicitly verify administrative privileges
      unless current_user&.admin?
        response.status = 403
        r.halt({ error: 'Forbidden: Admin access required' }.to_json)
      end

      User[id].destroy
      { status: 'success' }.to_json
    end
  end
end
end
end