class Faraday::Connection

conn.build_url("nigiri", :page => 2) # => https://sushi.com/api/nigiri?token=abc&page=2
conn.build_url("nigiri?page=2") # => https://sushi.com/api/nigiri?token=abc&page=2

conn.path_prefix # => "/api"
conn.scheme # => https
conn.url_prefix = "https://sushi.com/api?token=abc"
conn = Faraday::Connection.new { ... }

set on the connection instance.
Public: Takes a relative url for a request and combines it with the defaults

def build_url(url = nil, extra_params = nil)
  uri = build_exclusive_url(url)
  query_values = params.dup.merge_query(uri.query, options.params_encoder)
  query_values.update extra_params if extra_params
  uri.query = query_values.empty? ? nil : query_values.to_query(options.params_encoder)
  uri
end