Allow dynamic redirect uri from provider configuration

[ychaze]

By adding this to the strategy you can pass the redirect uri directly in the configuration of the provider.

For example, with devise in devise.rb:

Devise.setup do |config|

  config.omniauth :salesforce, 'key', 'secret', {redirect_uri: 'http://localhost:3000/users/auth/salesforce/callback'}

end

[ychaze]

@realdoug Is it possible that you merge it so we get the fix in the gem ?

[realdoug]

@yann Sorry about that. Testing now.

[realdoug]

I can't seem to break this. Merged. Will cut a new gem soon.

[ychaze]

Thanks!

[robvolk]

@realdoug can you cut a new gem? would like to use an official version instead of referencing it from github