README.md
# SignedForm
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SignedForm brings new convenience and security to your Rails 5 or Rails 4
application.
SignedForm is under active development. Please make sure you're reading the
README associated with the version of SignedForm you're using. Click the tag
link on GitHub to switch to the version you've installed to get the correct
README.
Or be brave and bundle the gem straight from GitHub master.
A nicely displayed version of this README complete with table of contents is
available [here](http://erichmenge.com/signed_form/).
## How It Works
Traditionally, when you create a form with Rails you enter your fields using
something like `f.text_field :name` and so on. Once you're done making your
form you need to make sure that you've set those parameters as accessible in the
model (Rails 3) or use `permit` (Rails 4). This is redundant. Why would you make
a form for a user to fill out and then not accept their input? You need to
always maintain this synchronization.
SignedForm generates a list of attributes that you have in your form and
attaches them to be submitted with the form along with a HMAC-SHA1 signature of
those attributes to protect them from tampering. That means no more `permit` and
no more `attr_accessible`. It just works.
What this looks like:
```erb
<%= form_for @user, signed: true do |f| %>
<% f.add_signed_fields :zipcode, :state # add additional fields to sign %>
<%= f.text_field :name %>
<%= f.text_field :address %>
<%= f.submit %>
<% end %>
```
```ruby
UsersController < ApplicationController
def update
@user = User.find params[:id]
@user.update_attributes params[:user]
end
end
```
Disabled fields need to be explicitly signed:
```erb
<%= form_for @user, signed: true do |f| %>
<% f.add_signed_fields :name %>
<%= f.text_field :name, disabled: true %>
<%= f.submit %>
<% end %>
```
That's it. You're done. Need to add a field? Pop it in the form. You don't need
to then update a list of attributes.
Of course, you're free to continue using the standard `form_for`. `SignedForm`
is strictly opt-in. It won't change the way you use standard forms.
## Is it any good?
Yes.
## More than just Convenience - Security
SignedForm protects you in 3 ways:
* Form fields are signed, so no alteration of the fields are allowed.
* Form actions are signed. That means a form with an action of `/admin/users/3`
will not work when submitted to `/users/3`.
* Form views are digested (see below). So if you remove a field from your form,
old forms will not be accepted despite a valid signature.
The second two methods of security are optional and can be turned off globally
or on a form by form basis.
## Requirements
SignedForm requires:
* Ruby 2.4.3 or 2.5.0
* Rails 4.2-stable, Rails 5.2-stable, or Rails master
[strong_parameters]: https://github.com/rails/strong_parameters
## Installation
Add this line to your application's Gemfile:
```ruby
gem 'signed_form'
```
And then execute:
$ bundle
You'll need to include `SignedForm::ActionController::PermitSignedParams` in the
controller(s) you want to use SignedForm with. This can be done application wide
by adding the `include` to your ApplicationController.
```ruby
ApplicationController < ActionController::Base
include SignedForm::ActionController::PermitSignedParams
# ...
end
```
## Support for other Builders
Any form that wraps `form_for` and the default field helpers will work with
SignedForm. For example, a signed SimpleForm might look like this:
```erb
<%= simple_form_for @user, signed: true do |f| %>
<%= f.input :name %>
<% end %>
```
This will create a signed form as expected.
For builders that don't use the standard field helpers under the hood, you can
create an adapter like this:
```ruby
class MyAdapter < SomeOtherBuilder
include SignedForm::FormBuilder
def some_helper(field, *other_args)
add_signed_fields field
super
end
end
```
Then in your view:
```erb
<%= form_for @user, signed: true, builder: MyAdapter do |f| %>
<%= f.some_helper :name %>
<% end %>
```
## ActiveAdmin support
Gem
[`signed_form-activeadmin`][] integrates SignedForm with Active Admin.
[`signed_form-activeadmin`]: https://github.com/cschramm/signed_form-activeadmin
## Form Digests
SignedForm will create a digest of all the views/partials involved with
rendering your form. If the form is modifed old forms will be expired. This is
done to eliminate the possibility of old forms coming back to bite you.
By default, there is a 5 minute grace period before old forms will be rejected.
This is done so that if you make a trivial change to a form you won't prevent a
form a user is currently filling out from being accepted when you restart your
server.
Of course if a critical mistake is made (such as allowing an admin field to be
set in the form) you could change the secret key to prevent any old form from
getting through.
By default, these digests are not cached. That means that each form that is
submitted will have the views be digested again. Most views and partials are
relatively small so the cost of computing the MD5 hash of the files is not very
expensive. However, if this is something you care about SignedForm also provides
a memory store (`SignedForm::DigestStores::MemoryStore`) that will cache the
digests in memory. Other stores could be used as well, as long as the object
responds to `#fetch` taking the cache key as an argument as well as the block
that will return the digest.
## Example Configuration
An example config/initializers/signed_form.rb might look something like this
(these are the defaults, with the exception of the key of course):
```ruby
SignedForm.config do |c|
c.options[:sign_destination] = true
c.options[:digest] = true
c.options[:digest_grace_period] = 300
c.options[:signed] = false # If true, sign all forms by default
c.digest_store = SignedForm::DigestStores::NullStore.new
c.secret_key = 'supersecret'
end
```
Those options that are in the options hash are the default per-form options.
They can be overridden by passing the same option to the `form_for` method.
## Testing Your Controllers
Because your tests won't include a signature you will get a
`ForbiddenAttributes` exception in your tests that do mass assignment.
SignedForm includes a test helper method, `permit_all_parameters` that works
with both TestUnit and RSpec.
Add `require 'signed_form/test_helper'` and `include SignedForm::TestHelper`
wherever appropriate for your tests. An example is below.
**Caution**: `permit_all_parameters` without a block modifies the singleton
class of the controller under test which lasts for the duration of the test. If
you want `permit_all_parameters` to be limited to a specific part of the test,
pass it a block and only that block will be affected. Example:
```ruby
describe CarsController do
include SignedForm::TestHelper
describe "POST create" do
it "should create a car" do
permit_all_parameters do
# This won't raise ForbiddenAttributesError
post :create, {:car => valid_attributes}, valid_session
end
# This one will raise
post :create, {:car => valid_attributes}, valid_session
# ...
end
end
end
```
Example without a block:
```ruby
describe CarsController do
include SignedForm::TestHelper
describe "POST create" do
before { permit_all_parameters }
describe "with valid params" do
it "assigns a newly created car as @car" do
post :create, {:car => valid_attributes}, valid_session
assigns(:car).should be_a(Car)
assigns(:car).should be_persisted
end
# ...
end
end
end
```
## I want to hear from you
If you're using SignedForm, I'd love to hear from you. What do you like? What
could be better? I'd love to hear your ideas. Join the mailing list on librelist
to join the discussion at [signedform@librelist.com][].
[signedform@librelist.com]: mailto:signedform@librelist.com
## Contributing
1. Fork it
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Add some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. Create new Pull Request