diff --git a/policy/diamond/policy/tiled/tiled.rego b/policy/diamond/policy/tiled/tiled.rego
index 783e7e7..f3c7cd8 100644
--- a/policy/diamond/policy/tiled/tiled.rego
+++ b/policy/diamond/policy/tiled/tiled.rego
@@ -32,57 +32,39 @@ user_session := to_number(_session) if {
 	_session
 }
 
+# service account check
 user_session := to_number(_session) if {
-	input.proposal in token.claims.subject.proposals
-}
-
-user_session := to_number(_session) if {
-	_session in token.claims.subject.sessions
-}
-
-user_session := to_number(_session) if {
-	input.beamline in beamlines
+	input.beamline == token.claims.beamline
 	input.beamline == session.beamline_for(input.proposal, input.visit)
 	_session in data.diamond.data.beamlines[input.beamline].sessions
 }
 
-default fedid := ""
-
-fedid := token.claims.fedid
-
 # Validates if the subject has permission to modify
 # the specific session in the input.
 default modify_session := false
 
 modify_session if session.access_session(
-	fedid,
+	token.claims.fedid,
 	data.diamond.data.sessions[input.session].proposal_number,
 	data.diamond.data.sessions[input.session].visit_number,
 )
 
+# service account check
 modify_session if {
-	data.diamond.data.sessions[input.session].proposal_number in token.claims.subject.proposals
-}
-
-modify_session if {
-	to_number(input.session) in token.claims.subject.sessions
-}
-
-modify_session if {
+	not token.claims.fedid
 	session.beamline_for(
 		data.diamond.data.sessions[input.session].proposal_number,
 		data.diamond.data.sessions[input.session].visit_number,
-	) in beamlines
+	) == token.claims.beamline
 }
 
-subject := data.diamond.data.subjects[token.claims.fedid] if token.claims.fedid
-
-else := token.claims.subject if token.claims.subject
+subject := data.diamond.data.subjects[token.claims.fedid]
 
 # Identifies all beamlines the subject is authorized to access
 # based on their assigned permissions.
 beamlines contains beamline if {
-	not admin.is_admin(fedid)
+	token.claims.fedid
+	not admin.is_admin(token.claims.fedid)
 	some p in subject.permissions
 	some beamline in object.get(data.diamond.data.admin, p, [])
 }
@@ -95,23 +77,33 @@ beamlines contains beamline if {
 # 2. Access via beamline-level permissions
 # 3. Access via proposal-level permissions
 user_sessions contains "*" if {
-	admin.is_admin(fedid)
+	subject
+	admin.is_admin(token.claims.fedid)
 }
 
 user_sessions contains to_number(session) if {
-	not admin.is_admin(fedid)
+	subject
+	not admin.is_admin(token.claims.fedid)
 	some session in subject.sessions
 }
 
 user_sessions contains to_number(session) if {
-	not admin.is_admin(fedid)
+	subject
+	not admin.is_admin(token.claims.fedid)
 	some beamline in beamlines
 	some session in data.diamond.data.beamlines[beamline].sessions
 }
 
 user_sessions contains to_number(session) if {
-	not admin.is_admin(fedid)
+	subject
+	not admin.is_admin(token.claims.fedid)
 	some p in subject.proposals
 	some i in data.diamond.data.proposals[format_int(p, 10)]
 	some session in i
 }
+
+# service account check
+user_sessions contains to_number(session) if {
+	not subject
+	some session in data.diamond.data.beamlines[token.claims.beamline].sessions
+}
diff --git a/policy/diamond/policy/tiled/tiled_test.rego b/policy/diamond/policy/tiled/tiled_test.rego
index a16b30c..3407d9c 100644
--- a/policy/diamond/policy/tiled/tiled_test.rego
+++ b/policy/diamond/policy/tiled/tiled_test.rego
@@ -131,72 +131,47 @@ test_modify_session if {
 
 # Service account tests
 
-test_user_session_allow_service_account_on_proposal if {
+test_user_session_allow_service_account_on_beamline if {
 	tiled.user_session == 11 with data.diamond.data as diamond_data
 		with input as {"beamline": "i03", "proposal": 1, "visit": 1}
-		with data.diamond.policy.token.claims as {"subject": {"proposals": [1], "sessions": [], "permissions": []}}
-}
-
-test_user_session_allow_service_account_on_session if {
-	tiled.user_session == 11 with data.diamond.data as diamond_data
-		with input as {"beamline": "i03", "proposal": 1, "visit": 1}
-		with data.diamond.policy.token.claims as {"subject": {"proposals": [], "sessions": [11], "permissions": []}}
+		with data.diamond.policy.token.claims as {"beamline": "i03"}
 }
 
 test_user_session_not_allow_service_account_wrong_beamline if {
 	not tiled.user_session with data.diamond.data as diamond_data
 		with input as {"beamline": "i03", "proposal": 1, "visit": 2}
-		with data.diamond.policy.token.claims as {"subject": {"proposals": [], "sessions": [], "permissions": ["b07_admin"]}}
+		with data.diamond.policy.token.claims as {"beamline": "b07"}
 }
 
-test_user_session_allow_service_account_with_beamline if {
-	tiled.user_session with data.diamond.data as diamond_data
-		with input as {"beamline": "b07", "proposal": 1, "visit": 2}
-		with data.diamond.policy.token.claims as {
-			"subject": {"proposals": [], "sessions": [], "permissions": ["b07_admin"]},
-			"fedid": "",
-		}
+test_user_session_not_allow_service_account_on_none_existent_beamline_beamline if {
+	not tiled.user_session with data.diamond.data as diamond_data
+		with input as {"beamline": "i03", "proposal": 1, "visit": 2}
+		with data.diamond.policy.token.claims as {"beamline": "b007"}
 }
 
-test_modify_session_on_proposal if {
+test_modify_session_on_beamline if {
 	tiled.modify_session with data.diamond.data as diamond_data
 		with input as {"session": "11"}
-		with data.diamond.policy.token.claims as {"subject": {"proposals": [1], "sessions": [], "permissions": []}}
+		with data.diamond.policy.token.claims as {"beamline": "i03"}
 }
 
-test_modify_session_on_session if {
-	tiled.modify_session with data.diamond.data as diamond_data
+test_modify_session_on_wrong_beamline if {
+	not tiled.modify_session with data.diamond.data as diamond_data
 		with input as {"session": "11"}
-		with data.diamond.policy.token.claims as {"subject": {"proposals": [], "sessions": [11], "permissions": []}}
+		with data.diamond.policy.token.claims as {"beamline": "b07"}
 }
 
-test_modify_session_on_permission if {
-	tiled.modify_session with data.diamond.data as diamond_data
-		with input as {"session": "12"}
-		with data.diamond.policy.token.claims as {"subject": {
-			"proposals": [],
-			"sessions": [],
-			"permissions": ["b07_admin"],
-		}}
+test_modify_session_on_none_existent_beamline if {
+	not tiled.modify_session with data.diamond.data as diamond_data
+		with input as {"session": "11"}
+		with data.diamond.policy.token.claims as {"beamline": "b007"}
 }
 
 test_user_session_tags_service_account if {
 	tiled.user_sessions == {11} with data.diamond.data as diamond_data
-		with data.diamond.policy.token.claims as {"subject": {
-			"proposals": [],
-			"sessions": [11],
-			"permissions": [],
-		}}
-	tiled.user_sessions == {11, 12} with data.diamond.data as diamond_data
-		with data.diamond.policy.token.claims as {"subject": {
-			"proposals": [1],
-			"sessions": [],
-			"permissions": [],
-		}}
+		with data.diamond.policy.token.claims as {"beamline": "i03"}
 	tiled.user_sessions == {12, 13, 14} with data.diamond.data as diamond_data
-		with data.diamond.policy.token.claims as {"subject": {
-			"proposals": [],
-			"sessions": [],
-			"permissions": ["b07_admin"],
-		}}
+		with data.diamond.policy.token.claims as {"beamline": "b07"}
+	tiled.user_sessions == set() with data.diamond.data as diamond_data
+		with data.diamond.policy.token.claims as {"beamline": "b007"}
 }