foo.go

func permWrapper(perms map[string][]string) server.HandlerWrapper { 
  return func(fn server.HandlerFunc) server.HandlerFunc {
    return func(ctx context.Context, req server.Request, rsp interface{}) error {
      md, ok := metadata.FromContext(ctx)
      if !ok {
        // just exec
        return fn(ctx, req, rsp)
      }
      role := md["role"]
      // check roles
      if roles, ok := perms[req.Method()]; ok {
        var authorised bool
        for _, r := roles {
          if r == role {
            authorised = true
            break
          }
        }
        
        // is authorised?
        if !authorised {
          return errors.Forbidden("go.micro.auth.error", "unauthorised role")
        }
      }
      // no perms for method
      return fn(ctx, req, rsp)
    }
  }
}

w := permWrapper(map[string][]string{
  "Foo.Bar": []string{"admin"},
})