Spec coverage and refactor for the api/v1/accounts controllers (#3451)

app/controllers/api/v1/accounts/credentials_controller.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class Api::V1::Accounts::CredentialsController < ApiController
+  before_action -> { doorkeeper_authorize! :write }, only: [:update]
+  before_action :require_user!
+
+  def show
+    @account = current_account
+    render 'api/v1/accounts/show'
+  end
+
+  def update
+    current_account.update!(account_params)
+    @account = current_account
+    render 'api/v1/accounts/show'
+  end
+
+  private
+
+  def account_params
+    params.permit(:display_name, :note, :avatar, :header)
+  end
+end