resolve_source

# File actionpack/lib/action_dispatch/http/content_security_policy.rb, line 268
      def resolve_source(source, context)
        case source
        when String
          source
        when Symbol
          source.to_s
        when Proc
          if context.nil?
            raise RuntimeError, "Missing context for the dynamic content security policy source: #{source.inspect}"
          else
            resolved = context.instance_exec(&source)
            resolved.is_a?(Symbol) ? apply_mapping(resolved) : resolved
          end
        else
          raise RuntimeError, "Unexpected content security policy source: #{source.inspect}"
        end
      end