diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 327e9e5b..e58a43cc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -57,7 +57,7 @@ jobs:
         python -m pip install --upgrade pip
         pip install bson
         pip install pymongo
-        pip install git+https://github.com/TeskaLabs/asab#egg=asab[storage_encryption]
+        pip install git+https://github.com/TeskaLabs/asab#egg=asab[encryption]
     
     - name: Test with unittest
       run: |
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d39ad869..3ad026a2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,8 @@
 - Allow unsetting some client features (#148, PLUM Sprint 230113)
 - OAuth 2.0 PKCE challenge (RFC7636) (#152, PLUM Sprint 230127)
 - Session tracking ID introduced (#135, PLUM Sprint 230210)
+- Clients can register a custom login_uri and login_key (#151, PLUM Sprint 230210)
+- Authorize request adds client_id to login URL query (#151, PLUM Sprint 230210)
 
 ### Refactoring
 - Regex validation of cookie_domain client attribute (#144, PLUM Sprint 230113)
diff --git a/seacatauth/authn/handler.py b/seacatauth/authn/handler.py
index 5f632bce..a5790663 100644
--- a/seacatauth/authn/handler.py
+++ b/seacatauth/authn/handler.py
@@ -59,11 +59,13 @@ async def login_prologue(self, request):
 		# Get arguments specified in login URL query
 		expiration = None
 		login_preferences = None
+		login_key = None
 		query_string = key.get("qs")
 		if query_string is not None:
 			query_dict = urllib.parse.parse_qs(query_string)
 
 			# Get requested session expiration
+			# TODO: This option should be moved to client config or removed completely
 			expiration = query_dict.get("expiration")
 			if expiration is not None:
 				try:
@@ -72,10 +74,16 @@ async def login_prologue(self, request):
 					L.warning("Error when parsing expiration: {}".format(e))
 
 			# Get preferred login descriptor IDs
+			# TODO: This option should be moved to client config or removed completely
 			login_preferences = query_dict.get("ldid")
 
+			# Get login key by client ID
+			client_id = query_dict.get("client_id")
+			if client_id is not None:
+				login_key = await self._get_client_login_key(client_id[0])
+
 		# Locate credentials
-		credentials_id = await self.CredentialsService.locate(ident, stop_at_first=True)
+		credentials_id = await self.CredentialsService.locate(ident, stop_at_first=True, key=login_key)
 		if credentials_id is None or credentials_id == []:
 			L.warning("Cannot locate credentials.", struct_data={"ident": ident})
 			# Empty credentials is used for creating a fake login session
@@ -128,7 +136,6 @@ async def login_prologue(self, request):
 		}
 		return asab.web.rest.json_response(request, response)
 
-
 	async def login(self, request):
 		lsid = request.match_info["lsid"]
 
@@ -271,7 +278,6 @@ async def smslogin(self, request):
 		body = {"result": "OK" if success is True else "FAILED"}
 		return aiohttp.web.Response(body=login_session.encrypt(body))
 
-
 	async def webauthn_login(self, request):
 		# Decode JSON request
 		lsid = request.match_info["lsid"]
@@ -303,3 +309,13 @@ async def webauthn_login(self, request):
 		await self.AuthenticationService.update_login_session(lsid, data=login_data)
 
 		return aiohttp.web.Response(body=login_session.encrypt(authentication_options))
+
+
+	async def _get_client_login_key(self, client_id):
+		client_service = self.AuthenticationService.App.get_service("seacatauth.ClientService")
+		try:
+			client = await client_service.get(client_id)
+			login_key = client.get("login_key")
+		except KeyError:
+			login_key = None
+		return login_key
diff --git a/seacatauth/client/service.py b/seacatauth/client/service.py
index 6e648a9d..5912527a 100644
--- a/seacatauth/client/service.py
+++ b/seacatauth/client/service.py
@@ -125,6 +125,15 @@
 	"login_uri": {  # NON-CANONICAL
 		"type": "string",
 		"description": "URL of preferred login page."},
+	"login_key": {  # NON-CANONICAL
+		"type": "object",
+		"description": "Additional data used for locating the credentials at login.",
+		"patternProperties": {
+			"^[a-zA-Z][a-zA-Z0-9_-]{0,126}[a-zA-Z0-9]$": {"anyOf": [
+				{"type": "string"},
+				{"type": "number"},
+				{"type": "boolean"},
+				{"type": "null"}]}}},
 	"template": {  # NON-CANONICAL
 		"type": "string",
 		"description": "Client template.",
@@ -339,7 +348,8 @@ async def register(
 
 		# Optional client metadata
 		for k in frozenset([
-			"client_name", "client_uri", "logout_uri", "cookie_domain", "custom_data", "login_uri", "template"]):
+			"client_name", "client_uri", "logout_uri", "cookie_domain", "custom_data", "login_uri", "login_key",
+			"template"]):
 			v = kwargs.get(k)
 			if v is not None and len(v) > 0:
 				upsertor.set(k, v)
diff --git a/seacatauth/credentials/providers/abc.py b/seacatauth/credentials/providers/abc.py
index 44f1f963..96b74f84 100644
--- a/seacatauth/credentials/providers/abc.py
+++ b/seacatauth/credentials/providers/abc.py
@@ -41,7 +41,7 @@ def get_info(self) -> dict:
 		}
 
 
-	async def locate(self, ident: str, ident_fields: dict = None) -> str:
+	async def locate(self, ident: str, ident_fields: dict = None, key: dict = None) -> str:
 		'''
 		Locate credentials based on the vague 'ident', which could be the username, password, phone number etc.
 		Return credentials_id or return None if not found.
diff --git a/seacatauth/credentials/providers/dictionary.py b/seacatauth/credentials/providers/dictionary.py
index e844b67a..7612a76e 100644
--- a/seacatauth/credentials/providers/dictionary.py
+++ b/seacatauth/credentials/providers/dictionary.py
@@ -108,7 +108,7 @@ async def delete(self, credentials_id) -> Optional[str]:
 		self.Dictionary.pop(credentials_id[len(prefix):])
 		return "OK"
 
-	async def locate(self, ident: str, ident_fields: dict = None) -> str:
+	async def locate(self, ident: str, ident_fields: dict = None, key: dict = None) -> str:
 		# TODO: Implement ident_fields support
 		# Fast match based on the username
 		credentials_id = hashlib.sha224(ident.encode('utf-8')).hexdigest()
diff --git a/seacatauth/credentials/providers/elasticsearch.py b/seacatauth/credentials/providers/elasticsearch.py
index 77de0ed2..033f127b 100644
--- a/seacatauth/credentials/providers/elasticsearch.py
+++ b/seacatauth/credentials/providers/elasticsearch.py
@@ -108,7 +108,7 @@ def _nomalize_credentials(self, username, user):
 		return obj
 
 
-	async def locate(self, ident: str, ident_fields: dict = None) -> str:
+	async def locate(self, ident: str, ident_fields: dict = None, key: dict = None) -> str:
 		query = {"query": {"bool": {
 			"filter": [
 				{"match_phrase": {"type": "user"}},
diff --git a/seacatauth/credentials/providers/htpasswd.py b/seacatauth/credentials/providers/htpasswd.py
index 567a6560..d1dbbe66 100644
--- a/seacatauth/credentials/providers/htpasswd.py
+++ b/seacatauth/credentials/providers/htpasswd.py
@@ -36,7 +36,7 @@ def __init__(self, provider_id, config_section_name):
 		self.HT = HtpasswdFile(self.Config['path'])
 
 
-	async def locate(self, ident: str, ident_fields: dict = None) -> str:
+	async def locate(self, ident: str, ident_fields: dict = None, key: dict = None) -> str:
 		# TODO: Implement ident_fields support
 		'''
 		Locate search for the exact match of provided ident and the username in the htpasswd file
diff --git a/seacatauth/credentials/providers/ldap.py b/seacatauth/credentials/providers/ldap.py
index f6de9d0e..c3a3ee8c 100644
--- a/seacatauth/credentials/providers/ldap.py
+++ b/seacatauth/credentials/providers/ldap.py
@@ -301,7 +301,7 @@ def _locate_worker(self, ident: str):
 		return None
 
 
-	async def locate(self, ident: str, ident_fields: dict = None) -> str:
+	async def locate(self, ident: str, ident_fields: dict = None, key: dict = None) -> str:
 		# TODO: Implement ident_fields support
 		'''
 		Locate search for the exact match of provided ident and the username in the htpasswd file
diff --git a/seacatauth/credentials/providers/mongodb.py b/seacatauth/credentials/providers/mongodb.py
index bb63f9ff..2f6876ac 100644
--- a/seacatauth/credentials/providers/mongodb.py
+++ b/seacatauth/credentials/providers/mongodb.py
@@ -208,7 +208,7 @@ async def delete(self, credentials_id) -> Optional[str]:
 		return "OK"
 
 
-	async def locate(self, ident: str, ident_fields: dict = None) -> Optional[str]:
+	async def locate(self, ident: str, ident_fields: dict = None, key: dict = None) -> Optional[str]:
 		"""
 		Locate credentials by matching ident string against configured ident fields.
 		"""
diff --git a/seacatauth/credentials/providers/mysql.py b/seacatauth/credentials/providers/mysql.py
index 95a5326b..4ed7d98d 100644
--- a/seacatauth/credentials/providers/mysql.py
+++ b/seacatauth/credentials/providers/mysql.py
@@ -70,10 +70,13 @@ def __init__(self, app, provider_id, config_section_name):
 			self.DataFields = None
 
 
-	async def locate(self, ident: str, ident_fields: dict = None) -> Optional[str]:
+	async def locate(self, ident: str, ident_fields: dict = None, key: dict = None) -> Optional[str]:
+		kwargs = {"ident": ident}
+		if key is not None:
+			kwargs.update(key)
 		async with aiomysql.connect(**self.ConnectionParams) as connection:
 			async with connection.cursor(aiomysql.DictCursor) as cursor:
-				await cursor.execute(self.LocateQuery, {"ident": ident})
+				await cursor.execute(self.LocateQuery, kwargs)
 				result = await cursor.fetchone()
 		if result is None:
 			return None
diff --git a/seacatauth/credentials/providers/xmongodb.py b/seacatauth/credentials/providers/xmongodb.py
index 9db7c118..ae09940b 100644
--- a/seacatauth/credentials/providers/xmongodb.py
+++ b/seacatauth/credentials/providers/xmongodb.py
@@ -85,8 +85,11 @@ def _prepare_query(self, query: str, query_args: dict):
 		return bson.json_util.loads(bound_query)
 
 
-	async def locate(self, ident: str, ident_fields: dict = None) -> Optional[str]:
-		query = self._prepare_query(self.LocateQuery, {"ident": ident})
+	async def locate(self, ident: str, ident_fields: dict = None, key: dict = None) -> Optional[str]:
+		kwargs = {"ident": ident}
+		if key is not None:
+			kwargs.update(key)
+		query = self._prepare_query(self.LocateQuery, kwargs)
 		cursor = self.Collection.aggregate(query)
 		result = None
 		async for obj in cursor:
diff --git a/seacatauth/credentials/service.py b/seacatauth/credentials/service.py
index 3132848e..e51b8ff8 100644
--- a/seacatauth/credentials/service.py
+++ b/seacatauth/credentials/service.py
@@ -133,13 +133,13 @@ def register_provider(self, credentials_provider):
 		self.CredentialProviders[credentials_provider.ProviderID] = credentials_provider
 
 
-	async def locate(self, ident: str, stop_at_first: bool = False):
+	async def locate(self, ident: str, stop_at_first: bool = False, key: dict = None):
 		'''
 		Locate credentials based on the vague 'ident', which could be the username, password, phone number etc.
 		'''
 		ident = ident.strip()
 		credentials_ids = []
-		pending = [provider.locate(ident, self.IdentFields) for provider in self.CredentialProviders.values()]
+		pending = [provider.locate(ident, self.IdentFields, key) for provider in self.CredentialProviders.values()]
 		while len(pending) > 0:
 			done, pending = await asyncio.wait(pending)
 			for task in done:
diff --git a/seacatauth/generic.py b/seacatauth/generic.py
index d27457ef..cfef4979 100644
--- a/seacatauth/generic.py
+++ b/seacatauth/generic.py
@@ -1,6 +1,6 @@
 import random
 import logging
-
+import urllib.parse
 import aiohttp.web
 import asab
 
@@ -137,6 +137,39 @@ async def nginx_introspection(
 	return response
 
 
+def urlparse(url: str):
+	"""
+	Parse the URL into a dictionary.
+
+	Convenience wrapper around urllib.parse.urlparse().
+	"""
+	return urllib.parse.urlparse(url)._asdict()
+
+
+def urlunparse(
+	*,
+	scheme: str = "",
+	netloc: str = "",
+	path: str = "",
+	params: str = "",
+	query: str = "",
+	fragment: str = ""
+):
+	"""
+	Build URL from individual components.
+
+	Convenience wrapper around urllib.parse.urlunparse().
+
+	Example usage:
+	```python
+	parsed = parse_url("http://local.test?option=true")
+	parsed["path"] = "/some/subpath"
+	url = unparse_url(**parsed)
+	```
+	"""
+	return urllib.parse.urlunparse((scheme, netloc, path, params, query, fragment))
+
+
 def generate_ergonomic_token(length: int):
 	'''
 	This function generates random string that is "ergonomic".
diff --git a/seacatauth/openidconnect/handler/authorize.py b/seacatauth/openidconnect/handler/authorize.py
index 8f8866e3..aaf692b1 100644
--- a/seacatauth/openidconnect/handler/authorize.py
+++ b/seacatauth/openidconnect/handler/authorize.py
@@ -12,6 +12,7 @@
 from ... import exceptions
 from ..utils import AuthErrorResponseCode
 from ..pkce import InvalidCodeChallengeMethodError
+from ...generic import urlparse, urlunparse
 
 #
 
@@ -479,12 +480,9 @@ async def reply_with_redirect_to_login(
 		)
 
 		login_query_params.append(("redirect_uri", authorize_redirect_uri))
+		login_query_params.append(("client_id", client_id))
 
-		login_url = "{}{}?{}".format(
-			self.AuthWebuiBaseUrl,
-			self.LoginPath,
-			urllib.parse.urlencode(login_query_params)
-		)
+		login_url = await self._build_login_uri(client_id, login_query_params)
 		response = aiohttp.web.HTTPNotFound(
 			headers={
 				"Location": login_url,
@@ -496,7 +494,6 @@ async def reply_with_redirect_to_login(
 		delete_cookie(self.App, response)
 		return response
 
-
 	async def reply_with_factor_setup_redirect(
 		self, session, missing_factors: list,
 		response_type: str, scope: list, client_id: str, redirect_uri: str,
@@ -560,7 +557,6 @@ async def reply_with_factor_setup_redirect(
 
 		return response
 
-
 	def reply_with_authentication_error(
 		self, error: str, redirect_uri: str,
 		error_description: str = None,
@@ -663,3 +659,33 @@ async def authorize_tenants_by_scope(self, scope, session, client_id):
 			raise exceptions.AccessDeniedError(subject=session.Credentials.Id)
 
 		return tenants
+
+
+	async def _build_login_uri(self, client_id, login_query_params):
+		"""
+		Check if the client has a registered login URI. If not, use the default.
+		Extend the URI with query parameters.
+		"""
+		try:
+			client_dict = await self.OpenIdConnectService.ClientService.get(client_id)
+			client_login_uri = client_dict.get("login_uri")
+		except KeyError:
+			client_login_uri = None
+		if client_login_uri is not None:
+			parsed = urlparse(client_login_uri)
+			query = urllib.parse.parse_qs(parsed["query"])
+			# WARNING: If the client's login URI includes query parameters with the same names
+			# as those used by Seacat Auth, they will be overwritten
+			query.update(login_query_params)
+			parsed["query"] = urllib.parse.urlencode(query)
+			login_url = urlunparse(**parsed)
+		else:
+			# Seacat Auth login expects the parameters to be at the end of the URL (in the fragment (hash) part)
+			# TODO: Consider using regular query parameters instead (UI refactoring needed)
+			#   so that Seacat Auth UI does not need a special approach here
+			login_url = "{}{}?{}".format(
+				self.AuthWebuiBaseUrl,
+				self.LoginPath,
+				urllib.parse.urlencode(login_query_params)
+			)
+		return login_url