After successfull sign up, call the sign in method of devise and pass required paramters to it

In my application I have used devise for registration purpose and it is working fine.

I have written another sign up method (I have to kept both the sign up methods) and able to register the user. Here is my code

new.html.haml

%h1 User Registration

= form_tag participant_user_registrations_path do
  = label_tag :full_name
  = text_field_tag :full_name

  = label_tag :address
  = text_area_tag :address, "", :rows => 5, :cols => 20

  = label_tag :mobile_number
  = text_field_tag :mobile_number

  = label_tag :email
  = text_field_tag :email

  = label_tag :slogan
  = text_area_tag :slogan, "", :rows => 5, :cols => 20

  = label_tag :password
  = password_field_tag :password

  = label_tag :activation_code
  = text_field_tag :activation_code

  = submit_tag "Sign Up", class: "btn btn-large btn-primary"

In my system username is auto-generated (we have a fixed format for it like full_name + mobile_no)

My user registration method

def another_registration
      @user = User.new(:client_id => 122,
                      :full_name => params["full_name"], 
                      :mobile_number => params["mobile_number"],
                      :address => params["address"],
                      :email => params["email"],
                      :participant_id => params["mobile_number"],
                      :status => "active",
                      :slogan => params["slogan"],
                      :password => params["password"])  
      if @user.save
        flash[:notice] = "User is saved"
      else
        flash[:alert] = @user.errors.full_messages.first #if @user.errors.any?
      end
    redirect_to :action => "new"
end

After successfully sign up I have to login the user account.

I have to use existing devise sign in functionality, so how can I call the devise sign in method and how to pass parameters to it.

Currently I am using username and password for the sign in.