message: Check empty input for login
diff: @@ -764,7 +764,11 @@ pub fn registry_login(
  .with_context(|| "failed to read stdin")?;
  // Automatically remove `cargo login` from an inputted token to
  // allow direct pastes from `registry.host()`/me.
  - line.replace("cargo login", "").trim().to_string()
  + line.replace("cargo login", "").trim().to_string();
  + if line.is_empty() {
  + bail!("please provide a non-empty token");
  + }
  + line
  }
  };
  