Incorrect @spec for authorize_url/2

[diogomrts]

I noticed that the @spec for the authorize_url/2 function in the Assent library is incorrect and does not match its actual return values. Specifically, the spec does not account for the {:error, term()} case, which causes issues with Dialyzer.

Current @SPEC

@spec authorize_url(Keyword.t(), module()) ::
  {:ok, %{session_params: %{state: binary()}, url: binary()}}

Actual Behavior

According to the implementation, the function can return either:

• {:ok, %{session_params: %{state: binary()}, url: binary()}}
• {:error, term()}

The @spec should reflect this, but currently, it only defines the {:ok, ...} case.

Steps to Reproduce

1. Use the authorize_url/2 function in a project with Dialyzer enabled.
2. Pattern match against {:error, _} in the function's return value.
3. Observe Dialyzer warnings indicating that the pattern {:error, _} can never match.