pattern_match_list.ex

def call(%Plug.Conn{req_headers: [{"authorization", token}]} = conn, _options) when is_binary(token) do
  # I want this to match
  conn
end

# this ends up matching
def call(conn, _), do: halt(conn)

conn = %{conn(:get, "/ping") | req_headers: [{"authorization", "asdf"}]}
call(conn) # matches the first, cool

conn = %{conn(:get, "/ping") | req_headers: [{"authorization", "asdf"}, {"foo", "bar"}]}
call(conn) # doesn't match first, but I want it to

# I guess I'm looking for something like -------------------v
def call(%Plug.Conn{req_headers: [{"authorization", token}, _]} = conn, _options)...
# or -------------------------------------------------------v
def call(%Plug.Conn{req_headers: [{"authorization", token}, *]} = conn, _options)...

# the following matches of course, but then I'd have to case against token being nil, which doesn't feel right.
def call(conn, _options) do                                      
  [token | _] = get_req_header(conn, "authorization")
  # do stuff with token
  conn
end

I think you can try %Plug.Conn{req_headers: [{"authorization", token} | other_headers]} = conn
EDIT:
This should be the equivalent of the match you are doing on https://gist.github.com/jc00ke/2261e927ffca77f16965b9a2d3c815d1#file-pattern_match_list-ex-L22

I am pretty sure you can't. Headers are a prop list and you can't match for an item in a list by its value, only by its position.