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+# 18 TACACS Based Authentication Support In OSM
+
+## Introduction 
+
+Terminal Access Controller Access-Control System (TACACS) refers to a family of related protocols handling remote authentication and related services for networked access control through a centralized server.
+
+OSM NB has a plugin which can interact with TACACS server to authenticate users.
+## Integration
+
+### Prerequisite for Integration
+   - TACACS host ip address reachable from OSM.
+   - TACACS server secret(or password).
+
+### Integration Steps
+   - Configure NBI to use TACACS plugin.
+      - Modifying nbi.cfg
+         - Set authentication.backend as tacacs in NBI/osm_nbi/nbi.cfg
+         - Set authentication.tacacs_host as TACACS host ip in NBI/osm_nbi/nbi.cfg
+         - Set authentication.tacacs_secret as TACACS server secret in NBI/osm_nbi/nbi.cfg
+
+## Testing Steps
+
+### Prerequisite for Testing
+   - Ensure users are present in TACACS server, which can be used for authentication.
+   - Configure OSM as mentioned above.
+
+### Testing
+   - Login with credentials present in TACACS server.
+   - OSM User with system_admin role or similar can assign project role mapping.
+   - TACACS users can log in using their credentials.
+
+## Limitations
+   - Since TACACS is used as read-only service, username update and password update shall not be allowed via OSM.
+     User credentials need to be updated by TACACS admin in TACACS to reflect.
+     However, OSM admin can handle project role assignment as required.
+     
+   - If user profile is removed from TACACS server, OSM still maintains the profile and will not be removed until next login.
+     As the profile is not available in TACACS, the authentication shall fail and user profile will be removed from OSM.
+     
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