Add support for access tokens using MAS (#83)

* Add support for access tokens using MAS

* use 1.13.0

* Update dependencies

* Harden auth credential selection in matrix link init

Use the same non-empty access-token criterion for auth mode selection and bind the token directly from the branch condition.
Return explicit configuration errors for missing or empty `device_id`/`password` instead of panicking, so invalid auth config fails gracefully.

* Centralize and harden user auth config handling

Move authentication-mode resolution into typed config parsing with ConfigUserAuth,
so downstream login setup consumes validated credentials instead of re-checking raw optional fields.

Enforce explicit password-vs-token selection, validate token/device/user-id requirements in one place,
and normalize empty auth env overrides to unset values for consistent behavior across YAML and environment input.

* Add auth config unit tests

Move auth_config tests into a dedicated cfg test module file to keep production config code compact while preserving behavior coverage. The tests cover password/token mode selection, missing/both auth method rejection, missing device_id, and empty-value handling.

* Use conventional mxlink version requirement

Replace the unconventional wildcard lower-bound expression with a standard semver lower bound for readability and tooling consistency.

---------

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

src/bot/load_config.rs

@@ -29,7 +29,15 @@ pub fn load() -> anyhow::Result<Config> {
             cfg_env::BAIBOT_HOMESERVER_SERVER_NAME => config.homeserver.server_name = value,
             cfg_env::BAIBOT_HOMESERVER_URL => config.homeserver.url = value,
             cfg_env::BAIBOT_USER_MXID_LOCALPART => config.user.mxid_localpart = value,
-            cfg_env::BAIBOT_USER_PASSWORD => config.user.password = value,
+            cfg_env::BAIBOT_USER_PASSWORD => {
+                config.user.password = optional_non_empty(value);
+            }
+            cfg_env::BAIBOT_USER_ACCESS_TOKEN => {
+                config.user.access_token = optional_non_empty(value);
+            }
+            cfg_env::BAIBOT_USER_DEVICE_ID => {
+                config.user.device_id = optional_non_empty(value);
+            }
             cfg_env::BAIBOT_USER_ENCRYPTION_RECOVERY_PASSPHRASE => {
                 config.user.encryption.recovery_passphrase = Some(value);
             }
@@ -120,3 +128,7 @@ pub fn load() -> anyhow::Result<Config> {
 
     Ok(config)
 }
+
+fn optional_non_empty(value: String) -> Option<String> {
+    if value.is_empty() { None } else { Some(value) }
+}