def credentials=(new_credentials)
      # Find new and changed properties.
      diff = new_credentials.inject([]) do |result, (key, value)|
        result << [key, value] if value != @credentials[key]
        result
      end

      # Find removed properties.
      diff = @credentials.inject(diff) do |result, (key, _)|
        result << [key, nil] unless new_credentials.include?(key)
        result
      end

      # Set each property.
      diff.each { |entry| set_credential(entry[0], entry[1]) }

      return nil
    end
def credentials=(new_credentials)
      # Find new and changed properties.
      diff = new_credentials.inject([]) do |result, (key, value)|
        result << [key, value] if value != @credentials[key]
        result
      end

      # Find removed properties.
      diff = @credentials.inject(diff) do |result, (key, _)|
        result << [key, nil] unless new_credentials.include?(key)
        result
      end

      # Set each property.
      diff.each { |entry| set_credential(entry[0], entry[1]) }

      return nil
    end
Set the credentials hash to a new one. Calculate difference, and call the
 AuthHandler callback appropriately.