diff --git a/backend/src/main/scala/industries/sunshine/planningpoker/Auth.scala b/backend/src/main/scala/industries/sunshine/planningpoker/Auth.scala
index d250e8e..47b6f57 100644
--- a/backend/src/main/scala/industries/sunshine/planningpoker/Auth.scala
+++ b/backend/src/main/scala/industries/sunshine/planningpoker/Auth.scala
@@ -10,6 +10,7 @@ import java.util.UUID
 import industries.sunshine.planningpoker.common.Models.{RoomID, Room}
 import org.http4s.ResponseCookie
 import cats.data.EitherT
+import scala.util.Random
 
 trait Auth[F[_]] {
 
@@ -29,7 +30,7 @@ trait Auth[F[_]] {
       roomPassword: String,
       nickName: String,
       nickPassword: String
-  ): F[Either[Unit, ResponseCookie]]
+  ): F[Either[String, ResponseCookie]]
 
   def deleteSession(
       sessionId: Long
@@ -70,16 +71,27 @@ object Auth {
       roomService: RoomService[F]
   ) extends Auth[F] {
 
+    val authcookie = "authcookie"
+
     override def joinRoom(
         roomName: String,
         roomPassword: String,
         nickName: String,
         nickPassword: String
-    ): F[Either[Unit, ResponseCookie]] = {
-      for {
-        joinedRoom <- roomService.joinRoom(RoomID(roomName), nickName, nickPassword, roomPassword)
-      } yield ()
-      ???
+    ): F[Either[String, ResponseCookie]] = {
+      // TODO check for existing session for same room
+      // and do i want to logout if existing session for another room? ugh
+      val roomId = RoomID(roomName)
+      val result = for {
+        playerId <- EitherT(
+          roomService.joinRoom(roomId, nickName, nickPassword, roomPassword)
+        )
+          .leftMap(_.toString())
+        newSessionId = Random.nextLong()
+        _ <- EitherT.liftF(sessions.update(_.updated(newSessionId, (roomId, playerId))))
+      } yield ResponseCookie(name = authcookie, content = newSessionId.toString(), secure = true)
+
+      result.value
     }
 
     override def authUser
diff --git a/backend/src/main/scala/industries/sunshine/planningpoker/RoomService.scala b/backend/src/main/scala/industries/sunshine/planningpoker/RoomService.scala
index 1da27c9..f1da656 100644
--- a/backend/src/main/scala/industries/sunshine/planningpoker/RoomService.scala
+++ b/backend/src/main/scala/industries/sunshine/planningpoker/RoomService.scala
@@ -20,7 +20,7 @@ trait RoomService[F[_]] {
       nickName: String,
       nickPassword: String,
       roomPassword: String
-  ): F[Either[RoomError, Room]]
+  ): F[Either[RoomError, PlayerID]]
   def deleteRoom(roomID: RoomID): F[Unit]
   def getRoom(roomID: RoomID): F[Option[Room]]
 }
@@ -49,8 +49,29 @@ class InMemoryRoomService[F[_]: Sync](stateRef: Ref[F, Map[RoomID, Room]]) exten
       nickName: String,
       nickPassword: String,
       roomPassword: String
-  ): F[Either[RoomError, Room]] = stateRef.modify[Either[RoomError, Room]] { rooms =>
-    val joinedRoom = for {
+  ): F[Either[RoomError, PlayerID]] = stateRef.modify { rooms =>
+    // need to cover cases:
+    // - player already present, then return as is, i guess
+    // - nick not known - add new player and new nick-password mapping
+    // - nick known - add new player
+
+    def addPlayer(room: Room): (PlayerID, Room) = {
+      room.players.find(_.name == nickName) match {
+        case Some(player) => player.id -> room
+        case None => // player is not present, but potentially was previously
+          val addingPlayer = Player.create(nickPassword)
+          val roomWithPlayer = room.copy(players = addingPlayer :: room.players)
+          room.playersPasswords.get(nickName) match {
+            case Some(_) => addingPlayer.id -> roomWithPlayer
+            case None =>
+              addingPlayer.id -> roomWithPlayer.copy(playersPasswords =
+                roomWithPlayer.playersPasswords.updated(nickName, nickPassword)
+              )
+          }
+      }
+    }
+
+    val joiningWithChecks = for {
       room <- rooms.get(id).toRight(RoomError.RoomMissing(id.name))
       _ <- Either.cond(room.password == roomPassword, (), RoomError.RoomPassIncorrect)
       isNickPassCorrect = room.playersPasswords
@@ -61,10 +82,10 @@ class InMemoryRoomService[F[_]: Sync](stateRef: Ref[F, Map[RoomID, Room]]) exten
         (),
         RoomError.NickPassIncorrect
       )
-      updatedRoom = room
-    } yield updatedRoom
+      (playerId, updatedRoom) = addPlayer(room)
+    } yield playerId
 
-    rooms -> joinedRoom
+    rooms -> joiningWithChecks
   }
 
 }
diff --git a/common/src/main/scala/industries/sunshine/planningpoker/Models.scala b/common/src/main/scala/industries/sunshine/planningpoker/Models.scala
index fc87f7a..ebab018 100644
--- a/common/src/main/scala/industries/sunshine/planningpoker/Models.scala
+++ b/common/src/main/scala/industries/sunshine/planningpoker/Models.scala
@@ -2,6 +2,7 @@ package industries.sunshine.planningpoker.common
 
 import java.util.UUID
 import io.circe._
+import scala.util.Random
 
 object Models {
 
@@ -53,6 +54,9 @@ object Models {
   final case class PlayerID(id: Long) derives Codec.AsObject
 
   final case class Player(name: String, id: PlayerID) derives Codec.AsObject
+  object Player {
+    def create(name: String) = Player(name, PlayerID(Random.nextLong))
+  }
 
   final case class RoomID(name: String) derives Codec.AsObject