diff --git a/src/database/key_value/rooms/state_accessor.rs b/src/database/key_value/rooms/state_accessor.rs
new file mode 100644
index 00000000..ae26a7c4
--- /dev/null
+++ b/src/database/key_value/rooms/state_accessor.rs
@@ -0,0 +1,160 @@
+    /// Builds a StateMap by iterating over all keys that start
+    /// with state_hash, this gives the full state for the given state_hash.
+    #[tracing::instrument(skip(self))]
+    pub async fn state_full_ids(&self, shortstatehash: u64) -> Result<BTreeMap<u64, Arc<EventId>>> {
+        let full_state = self
+            .load_shortstatehash_info(shortstatehash)?
+            .pop()
+            .expect("there is always one layer")
+            .1;
+        let mut result = BTreeMap::new();
+        let mut i = 0;
+        for compressed in full_state.into_iter() {
+            let parsed = self.parse_compressed_state_event(compressed)?;
+            result.insert(parsed.0, parsed.1);
+
+            i += 1;
+            if i % 100 == 0 {
+                tokio::task::yield_now().await;
+            }
+        }
+        Ok(result)
+    }
+
+    #[tracing::instrument(skip(self))]
+    pub async fn state_full(
+        &self,
+        shortstatehash: u64,
+    ) -> Result<HashMap<(StateEventType, String), Arc<PduEvent>>> {
+        let full_state = self
+            .load_shortstatehash_info(shortstatehash)?
+            .pop()
+            .expect("there is always one layer")
+            .1;
+
+        let mut result = HashMap::new();
+        let mut i = 0;
+        for compressed in full_state {
+            let (_, eventid) = self.parse_compressed_state_event(compressed)?;
+            if let Some(pdu) = self.get_pdu(&eventid)? {
+                result.insert(
+                    (
+                        pdu.kind.to_string().into(),
+                        pdu.state_key
+                            .as_ref()
+                            .ok_or_else(|| Error::bad_database("State event has no state key."))?
+                            .clone(),
+                    ),
+                    pdu,
+                );
+            }
+
+            i += 1;
+            if i % 100 == 0 {
+                tokio::task::yield_now().await;
+            }
+        }
+
+        Ok(result)
+    }
+
+    /// Returns a single PDU from `room_id` with key (`event_type`, `state_key`).
+    #[tracing::instrument(skip(self))]
+    pub fn state_get_id(
+        &self,
+        shortstatehash: u64,
+        event_type: &StateEventType,
+        state_key: &str,
+    ) -> Result<Option<Arc<EventId>>> {
+        let shortstatekey = match self.get_shortstatekey(event_type, state_key)? {
+            Some(s) => s,
+            None => return Ok(None),
+        };
+        let full_state = self
+            .load_shortstatehash_info(shortstatehash)?
+            .pop()
+            .expect("there is always one layer")
+            .1;
+        Ok(full_state
+            .into_iter()
+            .find(|bytes| bytes.starts_with(&shortstatekey.to_be_bytes()))
+            .and_then(|compressed| {
+                self.parse_compressed_state_event(compressed)
+                    .ok()
+                    .map(|(_, id)| id)
+            }))
+    }
+
+    /// Returns a single PDU from `room_id` with key (`event_type`, `state_key`).
+    #[tracing::instrument(skip(self))]
+    pub fn state_get(
+        &self,
+        shortstatehash: u64,
+        event_type: &StateEventType,
+        state_key: &str,
+    ) -> Result<Option<Arc<PduEvent>>> {
+        self.state_get_id(shortstatehash, event_type, state_key)?
+            .map_or(Ok(None), |event_id| self.get_pdu(&event_id))
+    }
+
+    /// Returns the state hash for this pdu.
+    pub fn pdu_shortstatehash(&self, event_id: &EventId) -> Result<Option<u64>> {
+        self.eventid_shorteventid
+            .get(event_id.as_bytes())?
+            .map_or(Ok(None), |shorteventid| {
+                self.shorteventid_shortstatehash
+                    .get(&shorteventid)?
+                    .map(|bytes| {
+                        utils::u64_from_bytes(&bytes).map_err(|_| {
+                            Error::bad_database(
+                                "Invalid shortstatehash bytes in shorteventid_shortstatehash",
+                            )
+                        })
+                    })
+                    .transpose()
+            })
+    }
+
+    /// Returns the full room state.
+    #[tracing::instrument(skip(self))]
+    pub async fn room_state_full(
+        &self,
+        room_id: &RoomId,
+    ) -> Result<HashMap<(StateEventType, String), Arc<PduEvent>>> {
+        if let Some(current_shortstatehash) = self.current_shortstatehash(room_id)? {
+            self.state_full(current_shortstatehash).await
+        } else {
+            Ok(HashMap::new())
+        }
+    }
+
+    /// Returns a single PDU from `room_id` with key (`event_type`, `state_key`).
+    #[tracing::instrument(skip(self))]
+    pub fn room_state_get_id(
+        &self,
+        room_id: &RoomId,
+        event_type: &StateEventType,
+        state_key: &str,
+    ) -> Result<Option<Arc<EventId>>> {
+        if let Some(current_shortstatehash) = self.current_shortstatehash(room_id)? {
+            self.state_get_id(current_shortstatehash, event_type, state_key)
+        } else {
+            Ok(None)
+        }
+    }
+
+    /// Returns a single PDU from `room_id` with key (`event_type`, `state_key`).
+    #[tracing::instrument(skip(self))]
+    pub fn room_state_get(
+        &self,
+        room_id: &RoomId,
+        event_type: &StateEventType,
+        state_key: &str,
+    ) -> Result<Option<Arc<PduEvent>>> {
+        if let Some(current_shortstatehash) = self.current_shortstatehash(room_id)? {
+            self.state_get(current_shortstatehash, event_type, state_key)
+        } else {
+            Ok(None)
+        }
+    }
+
diff --git a/src/database/key_value/rooms/user.rs b/src/database/key_value/rooms/user.rs
new file mode 100644
index 00000000..976ab5b3
--- /dev/null
+++ b/src/database/key_value/rooms/user.rs
@@ -0,0 +1,114 @@
+
+    #[tracing::instrument(skip(self))]
+    pub fn reset_notification_counts(&self, user_id: &UserId, room_id: &RoomId) -> Result<()> {
+        let mut userroom_id = user_id.as_bytes().to_vec();
+        userroom_id.push(0xff);
+        userroom_id.extend_from_slice(room_id.as_bytes());
+
+        self.userroomid_notificationcount
+            .insert(&userroom_id, &0_u64.to_be_bytes())?;
+        self.userroomid_highlightcount
+            .insert(&userroom_id, &0_u64.to_be_bytes())?;
+
+        Ok(())
+    }
+
+    #[tracing::instrument(skip(self))]
+    pub fn notification_count(&self, user_id: &UserId, room_id: &RoomId) -> Result<u64> {
+        let mut userroom_id = user_id.as_bytes().to_vec();
+        userroom_id.push(0xff);
+        userroom_id.extend_from_slice(room_id.as_bytes());
+
+        self.userroomid_notificationcount
+            .get(&userroom_id)?
+            .map(|bytes| {
+                utils::u64_from_bytes(&bytes)
+                    .map_err(|_| Error::bad_database("Invalid notification count in db."))
+            })
+            .unwrap_or(Ok(0))
+    }
+
+    #[tracing::instrument(skip(self))]
+    pub fn highlight_count(&self, user_id: &UserId, room_id: &RoomId) -> Result<u64> {
+        let mut userroom_id = user_id.as_bytes().to_vec();
+        userroom_id.push(0xff);
+        userroom_id.extend_from_slice(room_id.as_bytes());
+
+        self.userroomid_highlightcount
+            .get(&userroom_id)?
+            .map(|bytes| {
+                utils::u64_from_bytes(&bytes)
+                    .map_err(|_| Error::bad_database("Invalid highlight count in db."))
+            })
+            .unwrap_or(Ok(0))
+    }
+
+    pub fn associate_token_shortstatehash(
+        &self,
+        room_id: &RoomId,
+        token: u64,
+        shortstatehash: u64,
+    ) -> Result<()> {
+        let shortroomid = self.get_shortroomid(room_id)?.expect("room exists");
+
+        let mut key = shortroomid.to_be_bytes().to_vec();
+        key.extend_from_slice(&token.to_be_bytes());
+
+        self.roomsynctoken_shortstatehash
+            .insert(&key, &shortstatehash.to_be_bytes())
+    }
+
+    pub fn get_token_shortstatehash(&self, room_id: &RoomId, token: u64) -> Result<Option<u64>> {
+        let shortroomid = self.get_shortroomid(room_id)?.expect("room exists");
+
+        let mut key = shortroomid.to_be_bytes().to_vec();
+        key.extend_from_slice(&token.to_be_bytes());
+
+        self.roomsynctoken_shortstatehash
+            .get(&key)?
+            .map(|bytes| {
+                utils::u64_from_bytes(&bytes).map_err(|_| {
+                    Error::bad_database("Invalid shortstatehash in roomsynctoken_shortstatehash")
+                })
+            })
+            .transpose()
+    }
+
+    #[tracing::instrument(skip(self))]
+    pub fn get_shared_rooms<'a>(
+        &'a self,
+        users: Vec<Box<UserId>>,
+    ) -> Result<impl Iterator<Item = Result<Box<RoomId>>> + 'a> {
+        let iterators = users.into_iter().map(move |user_id| {
+            let mut prefix = user_id.as_bytes().to_vec();
+            prefix.push(0xff);
+
+            self.userroomid_joined
+                .scan_prefix(prefix)
+                .map(|(key, _)| {
+                    let roomid_index = key
+                        .iter()
+                        .enumerate()
+                        .find(|(_, &b)| b == 0xff)
+                        .ok_or_else(|| Error::bad_database("Invalid userroomid_joined in db."))?
+                        .0
+                        + 1; // +1 because the room id starts AFTER the separator
+
+                    let room_id = key[roomid_index..].to_vec();
+
+                    Ok::<_, Error>(room_id)
+                })
+                .filter_map(|r| r.ok())
+        });
+
+        // We use the default compare function because keys are sorted correctly (not reversed)
+        Ok(utils::common_elements(iterators, Ord::cmp)
+            .expect("users is not empty")
+            .map(|bytes| {
+                RoomId::parse(utils::string_from_bytes(&*bytes).map_err(|_| {
+                    Error::bad_database("Invalid RoomId bytes in userroomid_joined")
+                })?)
+                .map_err(|_| Error::bad_database("Invalid RoomId in userroomid_joined."))
+            }))
+    }
+
diff --git a/src/service/uiaa.rs b/src/database/key_value/uiaa.rs
similarity index 100%
rename from src/service/uiaa.rs
rename to src/database/key_value/uiaa.rs
diff --git a/src/service/rooms/state_accessor/data.rs b/src/service/rooms/state_accessor/data.rs
new file mode 100644
index 00000000..ae26a7c4
--- /dev/null
+++ b/src/service/rooms/state_accessor/data.rs
@@ -0,0 +1,160 @@
+    /// Builds a StateMap by iterating over all keys that start
+    /// with state_hash, this gives the full state for the given state_hash.
+    #[tracing::instrument(skip(self))]
+    pub async fn state_full_ids(&self, shortstatehash: u64) -> Result<BTreeMap<u64, Arc<EventId>>> {
+        let full_state = self
+            .load_shortstatehash_info(shortstatehash)?
+            .pop()
+            .expect("there is always one layer")
+            .1;
+        let mut result = BTreeMap::new();
+        let mut i = 0;
+        for compressed in full_state.into_iter() {
+            let parsed = self.parse_compressed_state_event(compressed)?;
+            result.insert(parsed.0, parsed.1);
+
+            i += 1;
+            if i % 100 == 0 {
+                tokio::task::yield_now().await;
+            }
+        }
+        Ok(result)
+    }
+
+    #[tracing::instrument(skip(self))]
+    pub async fn state_full(
+        &self,
+        shortstatehash: u64,
+    ) -> Result<HashMap<(StateEventType, String), Arc<PduEvent>>> {
+        let full_state = self
+            .load_shortstatehash_info(shortstatehash)?
+            .pop()
+            .expect("there is always one layer")
+            .1;
+
+        let mut result = HashMap::new();
+        let mut i = 0;
+        for compressed in full_state {
+            let (_, eventid) = self.parse_compressed_state_event(compressed)?;
+            if let Some(pdu) = self.get_pdu(&eventid)? {
+                result.insert(
+                    (
+                        pdu.kind.to_string().into(),
+                        pdu.state_key
+                            .as_ref()
+                            .ok_or_else(|| Error::bad_database("State event has no state key."))?
+                            .clone(),
+                    ),
+                    pdu,
+                );
+            }
+
+            i += 1;
+            if i % 100 == 0 {
+                tokio::task::yield_now().await;
+            }
+        }
+
+        Ok(result)
+    }
+
+    /// Returns a single PDU from `room_id` with key (`event_type`, `state_key`).
+    #[tracing::instrument(skip(self))]
+    pub fn state_get_id(
+        &self,
+        shortstatehash: u64,
+        event_type: &StateEventType,
+        state_key: &str,
+    ) -> Result<Option<Arc<EventId>>> {
+        let shortstatekey = match self.get_shortstatekey(event_type, state_key)? {
+            Some(s) => s,
+            None => return Ok(None),
+        };
+        let full_state = self
+            .load_shortstatehash_info(shortstatehash)?
+            .pop()
+            .expect("there is always one layer")
+            .1;
+        Ok(full_state
+            .into_iter()
+            .find(|bytes| bytes.starts_with(&shortstatekey.to_be_bytes()))
+            .and_then(|compressed| {
+                self.parse_compressed_state_event(compressed)
+                    .ok()
+                    .map(|(_, id)| id)
+            }))
+    }
+
+    /// Returns a single PDU from `room_id` with key (`event_type`, `state_key`).
+    #[tracing::instrument(skip(self))]
+    pub fn state_get(
+        &self,
+        shortstatehash: u64,
+        event_type: &StateEventType,
+        state_key: &str,
+    ) -> Result<Option<Arc<PduEvent>>> {
+        self.state_get_id(shortstatehash, event_type, state_key)?
+            .map_or(Ok(None), |event_id| self.get_pdu(&event_id))
+    }
+
+    /// Returns the state hash for this pdu.
+    pub fn pdu_shortstatehash(&self, event_id: &EventId) -> Result<Option<u64>> {
+        self.eventid_shorteventid
+            .get(event_id.as_bytes())?
+            .map_or(Ok(None), |shorteventid| {
+                self.shorteventid_shortstatehash
+                    .get(&shorteventid)?
+                    .map(|bytes| {
+                        utils::u64_from_bytes(&bytes).map_err(|_| {
+                            Error::bad_database(
+                                "Invalid shortstatehash bytes in shorteventid_shortstatehash",
+                            )
+                        })
+                    })
+                    .transpose()
+            })
+    }
+
+    /// Returns the full room state.
+    #[tracing::instrument(skip(self))]
+    pub async fn room_state_full(
+        &self,
+        room_id: &RoomId,
+    ) -> Result<HashMap<(StateEventType, String), Arc<PduEvent>>> {
+        if let Some(current_shortstatehash) = self.current_shortstatehash(room_id)? {
+            self.state_full(current_shortstatehash).await
+        } else {
+            Ok(HashMap::new())
+        }
+    }
+
+    /// Returns a single PDU from `room_id` with key (`event_type`, `state_key`).
+    #[tracing::instrument(skip(self))]
+    pub fn room_state_get_id(
+        &self,
+        room_id: &RoomId,
+        event_type: &StateEventType,
+        state_key: &str,
+    ) -> Result<Option<Arc<EventId>>> {
+        if let Some(current_shortstatehash) = self.current_shortstatehash(room_id)? {
+            self.state_get_id(current_shortstatehash, event_type, state_key)
+        } else {
+            Ok(None)
+        }
+    }
+
+    /// Returns a single PDU from `room_id` with key (`event_type`, `state_key`).
+    #[tracing::instrument(skip(self))]
+    pub fn room_state_get(
+        &self,
+        room_id: &RoomId,
+        event_type: &StateEventType,
+        state_key: &str,
+    ) -> Result<Option<Arc<PduEvent>>> {
+        if let Some(current_shortstatehash) = self.current_shortstatehash(room_id)? {
+            self.state_get(current_shortstatehash, event_type, state_key)
+        } else {
+            Ok(None)
+        }
+    }
+
diff --git a/src/service/rooms/user/data.rs b/src/service/rooms/user/data.rs
new file mode 100644
index 00000000..976ab5b3
--- /dev/null
+++ b/src/service/rooms/user/data.rs
@@ -0,0 +1,114 @@
+
+    #[tracing::instrument(skip(self))]
+    pub fn reset_notification_counts(&self, user_id: &UserId, room_id: &RoomId) -> Result<()> {
+        let mut userroom_id = user_id.as_bytes().to_vec();
+        userroom_id.push(0xff);
+        userroom_id.extend_from_slice(room_id.as_bytes());
+
+        self.userroomid_notificationcount
+            .insert(&userroom_id, &0_u64.to_be_bytes())?;
+        self.userroomid_highlightcount
+            .insert(&userroom_id, &0_u64.to_be_bytes())?;
+
+        Ok(())
+    }
+
+    #[tracing::instrument(skip(self))]
+    pub fn notification_count(&self, user_id: &UserId, room_id: &RoomId) -> Result<u64> {
+        let mut userroom_id = user_id.as_bytes().to_vec();
+        userroom_id.push(0xff);
+        userroom_id.extend_from_slice(room_id.as_bytes());
+
+        self.userroomid_notificationcount
+            .get(&userroom_id)?
+            .map(|bytes| {
+                utils::u64_from_bytes(&bytes)
+                    .map_err(|_| Error::bad_database("Invalid notification count in db."))
+            })
+            .unwrap_or(Ok(0))
+    }
+
+    #[tracing::instrument(skip(self))]
+    pub fn highlight_count(&self, user_id: &UserId, room_id: &RoomId) -> Result<u64> {
+        let mut userroom_id = user_id.as_bytes().to_vec();
+        userroom_id.push(0xff);
+        userroom_id.extend_from_slice(room_id.as_bytes());
+
+        self.userroomid_highlightcount
+            .get(&userroom_id)?
+            .map(|bytes| {
+                utils::u64_from_bytes(&bytes)
+                    .map_err(|_| Error::bad_database("Invalid highlight count in db."))
+            })
+            .unwrap_or(Ok(0))
+    }
+
+    pub fn associate_token_shortstatehash(
+        &self,
+        room_id: &RoomId,
+        token: u64,
+        shortstatehash: u64,
+    ) -> Result<()> {
+        let shortroomid = self.get_shortroomid(room_id)?.expect("room exists");
+
+        let mut key = shortroomid.to_be_bytes().to_vec();
+        key.extend_from_slice(&token.to_be_bytes());
+
+        self.roomsynctoken_shortstatehash
+            .insert(&key, &shortstatehash.to_be_bytes())
+    }
+
+    pub fn get_token_shortstatehash(&self, room_id: &RoomId, token: u64) -> Result<Option<u64>> {
+        let shortroomid = self.get_shortroomid(room_id)?.expect("room exists");
+
+        let mut key = shortroomid.to_be_bytes().to_vec();
+        key.extend_from_slice(&token.to_be_bytes());
+
+        self.roomsynctoken_shortstatehash
+            .get(&key)?
+            .map(|bytes| {
+                utils::u64_from_bytes(&bytes).map_err(|_| {
+                    Error::bad_database("Invalid shortstatehash in roomsynctoken_shortstatehash")
+                })
+            })
+            .transpose()
+    }
+
+    #[tracing::instrument(skip(self))]
+    pub fn get_shared_rooms<'a>(
+        &'a self,
+        users: Vec<Box<UserId>>,
+    ) -> Result<impl Iterator<Item = Result<Box<RoomId>>> + 'a> {
+        let iterators = users.into_iter().map(move |user_id| {
+            let mut prefix = user_id.as_bytes().to_vec();
+            prefix.push(0xff);
+
+            self.userroomid_joined
+                .scan_prefix(prefix)
+                .map(|(key, _)| {
+                    let roomid_index = key
+                        .iter()
+                        .enumerate()
+                        .find(|(_, &b)| b == 0xff)
+                        .ok_or_else(|| Error::bad_database("Invalid userroomid_joined in db."))?
+                        .0
+                        + 1; // +1 because the room id starts AFTER the separator
+
+                    let room_id = key[roomid_index..].to_vec();
+
+                    Ok::<_, Error>(room_id)
+                })
+                .filter_map(|r| r.ok())
+        });
+
+        // We use the default compare function because keys are sorted correctly (not reversed)
+        Ok(utils::common_elements(iterators, Ord::cmp)
+            .expect("users is not empty")
+            .map(|bytes| {
+                RoomId::parse(utils::string_from_bytes(&*bytes).map_err(|_| {
+                    Error::bad_database("Invalid RoomId bytes in userroomid_joined")
+                })?)
+                .map_err(|_| Error::bad_database("Invalid RoomId in userroomid_joined."))
+            }))
+    }
+
diff --git a/src/service/uiaa/data.rs b/src/service/uiaa/data.rs
new file mode 100644
index 00000000..12373139
--- /dev/null
+++ b/src/service/uiaa/data.rs
@@ -0,0 +1,227 @@
+use std::{
+    collections::BTreeMap,
+    sync::{Arc, RwLock},
+};
+
+use crate::{client_server::SESSION_ID_LENGTH, utils, Error, Result};
+use ruma::{
+    api::client::{
+        error::ErrorKind,
+        uiaa::{
+            AuthType, IncomingAuthData, IncomingPassword,
+            IncomingUserIdentifier::UserIdOrLocalpart, UiaaInfo,
+        },
+    },
+    signatures::CanonicalJsonValue,
+    DeviceId, UserId,
+};
+use tracing::error;
+
+use super::abstraction::Tree;
+
+pub struct Uiaa {
+    pub(super) userdevicesessionid_uiaainfo: Arc<dyn Tree>, // User-interactive authentication
+    pub(super) userdevicesessionid_uiaarequest:
+        RwLock<BTreeMap<(Box<UserId>, Box<DeviceId>, String), CanonicalJsonValue>>,
+}
+
+impl Uiaa {
+    /// Creates a new Uiaa session. Make sure the session token is unique.
+    pub fn create(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        uiaainfo: &UiaaInfo,
+        json_body: &CanonicalJsonValue,
+    ) -> Result<()> {
+        self.set_uiaa_request(
+            user_id,
+            device_id,
+            uiaainfo.session.as_ref().expect("session should be set"), // TODO: better session error handling (why is it optional in ruma?)
+            json_body,
+        )?;
+        self.update_uiaa_session(
+            user_id,
+            device_id,
+            uiaainfo.session.as_ref().expect("session should be set"),
+            Some(uiaainfo),
+        )
+    }
+
+    pub fn try_auth(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        auth: &IncomingAuthData,
+        uiaainfo: &UiaaInfo,
+        users: &super::users::Users,
+        globals: &super::globals::Globals,
+    ) -> Result<(bool, UiaaInfo)> {
+        let mut uiaainfo = auth
+            .session()
+            .map(|session| self.get_uiaa_session(user_id, device_id, session))
+            .unwrap_or_else(|| Ok(uiaainfo.clone()))?;
+
+        if uiaainfo.session.is_none() {
+            uiaainfo.session = Some(utils::random_string(SESSION_ID_LENGTH));
+        }
+
+        match auth {
+            // Find out what the user completed
+            IncomingAuthData::Password(IncomingPassword {
+                identifier,
+                password,
+                ..
+            }) => {
+                let username = match identifier {
+                    UserIdOrLocalpart(username) => username,
+                    _ => {
+                        return Err(Error::BadRequest(
+                            ErrorKind::Unrecognized,
+                            "Identifier type not recognized.",
+                        ))
+                    }
+                };
+
+                let user_id =
+                    UserId::parse_with_server_name(username.clone(), globals.server_name())
+                        .map_err(|_| {
+                            Error::BadRequest(ErrorKind::InvalidParam, "User ID is invalid.")
+                        })?;
+
+                // Check if password is correct
+                if let Some(hash) = users.password_hash(&user_id)? {
+                    let hash_matches =
+                        argon2::verify_encoded(&hash, password.as_bytes()).unwrap_or(false);
+
+                    if !hash_matches {
+                        uiaainfo.auth_error = Some(ruma::api::client::error::ErrorBody {
+                            kind: ErrorKind::Forbidden,
+                            message: "Invalid username or password.".to_owned(),
+                        });
+                        return Ok((false, uiaainfo));
+                    }
+                }
+
+                // Password was correct! Let's add it to `completed`
+                uiaainfo.completed.push(AuthType::Password);
+            }
+            IncomingAuthData::Dummy(_) => {
+                uiaainfo.completed.push(AuthType::Dummy);
+            }
+            k => error!("type not supported: {:?}", k),
+        }
+
+        // Check if a flow now succeeds
+        let mut completed = false;
+        'flows: for flow in &mut uiaainfo.flows {
+            for stage in &flow.stages {
+                if !uiaainfo.completed.contains(stage) {
+                    continue 'flows;
+                }
+            }
+            // We didn't break, so this flow succeeded!
+            completed = true;
+        }
+
+        if !completed {
+            self.update_uiaa_session(
+                user_id,
+                device_id,
+                uiaainfo.session.as_ref().expect("session is always set"),
+                Some(&uiaainfo),
+            )?;
+            return Ok((false, uiaainfo));
+        }
+
+        // UIAA was successful! Remove this session and return true
+        self.update_uiaa_session(
+            user_id,
+            device_id,
+            uiaainfo.session.as_ref().expect("session is always set"),
+            None,
+        )?;
+        Ok((true, uiaainfo))
+    }
+
+    fn set_uiaa_request(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        session: &str,
+        request: &CanonicalJsonValue,
+    ) -> Result<()> {
+        self.userdevicesessionid_uiaarequest
+            .write()
+            .unwrap()
+            .insert(
+                (user_id.to_owned(), device_id.to_owned(), session.to_owned()),
+                request.to_owned(),
+            );
+
+        Ok(())
+    }
+
+    pub fn get_uiaa_request(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        session: &str,
+    ) -> Option<CanonicalJsonValue> {
+        self.userdevicesessionid_uiaarequest
+            .read()
+            .unwrap()
+            .get(&(user_id.to_owned(), device_id.to_owned(), session.to_owned()))
+            .map(|j| j.to_owned())
+    }
+
+    fn update_uiaa_session(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        session: &str,
+        uiaainfo: Option<&UiaaInfo>,
+    ) -> Result<()> {
+        let mut userdevicesessionid = user_id.as_bytes().to_vec();
+        userdevicesessionid.push(0xff);
+        userdevicesessionid.extend_from_slice(device_id.as_bytes());
+        userdevicesessionid.push(0xff);
+        userdevicesessionid.extend_from_slice(session.as_bytes());
+
+        if let Some(uiaainfo) = uiaainfo {
+            self.userdevicesessionid_uiaainfo.insert(
+                &userdevicesessionid,
+                &serde_json::to_vec(&uiaainfo).expect("UiaaInfo::to_vec always works"),
+            )?;
+        } else {
+            self.userdevicesessionid_uiaainfo
+                .remove(&userdevicesessionid)?;
+        }
+
+        Ok(())
+    }
+
+    fn get_uiaa_session(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        session: &str,
+    ) -> Result<UiaaInfo> {
+        let mut userdevicesessionid = user_id.as_bytes().to_vec();
+        userdevicesessionid.push(0xff);
+        userdevicesessionid.extend_from_slice(device_id.as_bytes());
+        userdevicesessionid.push(0xff);
+        userdevicesessionid.extend_from_slice(session.as_bytes());
+
+        serde_json::from_slice(
+            &self
+                .userdevicesessionid_uiaainfo
+                .get(&userdevicesessionid)?
+                .ok_or(Error::BadRequest(
+                    ErrorKind::Forbidden,
+                    "UIAA session does not exist.",
+                ))?,
+        )
+        .map_err(|_| Error::bad_database("UiaaInfo in userdeviceid_uiaainfo is invalid."))
+    }
+}
diff --git a/src/service/uiaa/mod.rs b/src/service/uiaa/mod.rs
new file mode 100644
index 00000000..12373139
--- /dev/null
+++ b/src/service/uiaa/mod.rs
@@ -0,0 +1,227 @@
+use std::{
+    collections::BTreeMap,
+    sync::{Arc, RwLock},
+};
+
+use crate::{client_server::SESSION_ID_LENGTH, utils, Error, Result};
+use ruma::{
+    api::client::{
+        error::ErrorKind,
+        uiaa::{
+            AuthType, IncomingAuthData, IncomingPassword,
+            IncomingUserIdentifier::UserIdOrLocalpart, UiaaInfo,
+        },
+    },
+    signatures::CanonicalJsonValue,
+    DeviceId, UserId,
+};
+use tracing::error;
+
+use super::abstraction::Tree;
+
+pub struct Uiaa {
+    pub(super) userdevicesessionid_uiaainfo: Arc<dyn Tree>, // User-interactive authentication
+    pub(super) userdevicesessionid_uiaarequest:
+        RwLock<BTreeMap<(Box<UserId>, Box<DeviceId>, String), CanonicalJsonValue>>,
+}
+
+impl Uiaa {
+    /// Creates a new Uiaa session. Make sure the session token is unique.
+    pub fn create(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        uiaainfo: &UiaaInfo,
+        json_body: &CanonicalJsonValue,
+    ) -> Result<()> {
+        self.set_uiaa_request(
+            user_id,
+            device_id,
+            uiaainfo.session.as_ref().expect("session should be set"), // TODO: better session error handling (why is it optional in ruma?)
+            json_body,
+        )?;
+        self.update_uiaa_session(
+            user_id,
+            device_id,
+            uiaainfo.session.as_ref().expect("session should be set"),
+            Some(uiaainfo),
+        )
+    }
+
+    pub fn try_auth(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        auth: &IncomingAuthData,
+        uiaainfo: &UiaaInfo,
+        users: &super::users::Users,
+        globals: &super::globals::Globals,
+    ) -> Result<(bool, UiaaInfo)> {
+        let mut uiaainfo = auth
+            .session()
+            .map(|session| self.get_uiaa_session(user_id, device_id, session))
+            .unwrap_or_else(|| Ok(uiaainfo.clone()))?;
+
+        if uiaainfo.session.is_none() {
+            uiaainfo.session = Some(utils::random_string(SESSION_ID_LENGTH));
+        }
+
+        match auth {
+            // Find out what the user completed
+            IncomingAuthData::Password(IncomingPassword {
+                identifier,
+                password,
+                ..
+            }) => {
+                let username = match identifier {
+                    UserIdOrLocalpart(username) => username,
+                    _ => {
+                        return Err(Error::BadRequest(
+                            ErrorKind::Unrecognized,
+                            "Identifier type not recognized.",
+                        ))
+                    }
+                };
+
+                let user_id =
+                    UserId::parse_with_server_name(username.clone(), globals.server_name())
+                        .map_err(|_| {
+                            Error::BadRequest(ErrorKind::InvalidParam, "User ID is invalid.")
+                        })?;
+
+                // Check if password is correct
+                if let Some(hash) = users.password_hash(&user_id)? {
+                    let hash_matches =
+                        argon2::verify_encoded(&hash, password.as_bytes()).unwrap_or(false);
+
+                    if !hash_matches {
+                        uiaainfo.auth_error = Some(ruma::api::client::error::ErrorBody {
+                            kind: ErrorKind::Forbidden,
+                            message: "Invalid username or password.".to_owned(),
+                        });
+                        return Ok((false, uiaainfo));
+                    }
+                }
+
+                // Password was correct! Let's add it to `completed`
+                uiaainfo.completed.push(AuthType::Password);
+            }
+            IncomingAuthData::Dummy(_) => {
+                uiaainfo.completed.push(AuthType::Dummy);
+            }
+            k => error!("type not supported: {:?}", k),
+        }
+
+        // Check if a flow now succeeds
+        let mut completed = false;
+        'flows: for flow in &mut uiaainfo.flows {
+            for stage in &flow.stages {
+                if !uiaainfo.completed.contains(stage) {
+                    continue 'flows;
+                }
+            }
+            // We didn't break, so this flow succeeded!
+            completed = true;
+        }
+
+        if !completed {
+            self.update_uiaa_session(
+                user_id,
+                device_id,
+                uiaainfo.session.as_ref().expect("session is always set"),
+                Some(&uiaainfo),
+            )?;
+            return Ok((false, uiaainfo));
+        }
+
+        // UIAA was successful! Remove this session and return true
+        self.update_uiaa_session(
+            user_id,
+            device_id,
+            uiaainfo.session.as_ref().expect("session is always set"),
+            None,
+        )?;
+        Ok((true, uiaainfo))
+    }
+
+    fn set_uiaa_request(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        session: &str,
+        request: &CanonicalJsonValue,
+    ) -> Result<()> {
+        self.userdevicesessionid_uiaarequest
+            .write()
+            .unwrap()
+            .insert(
+                (user_id.to_owned(), device_id.to_owned(), session.to_owned()),
+                request.to_owned(),
+            );
+
+        Ok(())
+    }
+
+    pub fn get_uiaa_request(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        session: &str,
+    ) -> Option<CanonicalJsonValue> {
+        self.userdevicesessionid_uiaarequest
+            .read()
+            .unwrap()
+            .get(&(user_id.to_owned(), device_id.to_owned(), session.to_owned()))
+            .map(|j| j.to_owned())
+    }
+
+    fn update_uiaa_session(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        session: &str,
+        uiaainfo: Option<&UiaaInfo>,
+    ) -> Result<()> {
+        let mut userdevicesessionid = user_id.as_bytes().to_vec();
+        userdevicesessionid.push(0xff);
+        userdevicesessionid.extend_from_slice(device_id.as_bytes());
+        userdevicesessionid.push(0xff);
+        userdevicesessionid.extend_from_slice(session.as_bytes());
+
+        if let Some(uiaainfo) = uiaainfo {
+            self.userdevicesessionid_uiaainfo.insert(
+                &userdevicesessionid,
+                &serde_json::to_vec(&uiaainfo).expect("UiaaInfo::to_vec always works"),
+            )?;
+        } else {
+            self.userdevicesessionid_uiaainfo
+                .remove(&userdevicesessionid)?;
+        }
+
+        Ok(())
+    }
+
+    fn get_uiaa_session(
+        &self,
+        user_id: &UserId,
+        device_id: &DeviceId,
+        session: &str,
+    ) -> Result<UiaaInfo> {
+        let mut userdevicesessionid = user_id.as_bytes().to_vec();
+        userdevicesessionid.push(0xff);
+        userdevicesessionid.extend_from_slice(device_id.as_bytes());
+        userdevicesessionid.push(0xff);
+        userdevicesessionid.extend_from_slice(session.as_bytes());
+
+        serde_json::from_slice(
+            &self
+                .userdevicesessionid_uiaainfo
+                .get(&userdevicesessionid)?
+                .ok_or(Error::BadRequest(
+                    ErrorKind::Forbidden,
+                    "UIAA session does not exist.",
+                ))?,
+        )
+        .map_err(|_| Error::bad_database("UiaaInfo in userdeviceid_uiaainfo is invalid."))
+    }
+}