Replace appservice auth with MAS OAuth 2.0 device grant

The appservice approach was wrong for a /sync bot: Synapse forbids appservice-namespace users from /sync (sync.py raises NotImplementedError, 'we no longer support AS users using /sync'), so the bot received no events. Authenticate instead via the MAS OAuth 2.0 device grant (RFC 8628): - internal/bot/masauth.go: discover MAS endpoints from well-known+OIDC, dynamic client registration, device-code flow (prints approval URL once), persist rotating refresh token in data/mas_auth.json, refresh access token. - internal/bot/client.go: obtain token via device grant, keep bot a NORMAL user (so /sync works), background refresher updates the live client, E2EE via cryptohelper on a fresh device. - main.go: drop AS_TOKEN; remove registration.yaml.example; docs updated. First run needs a one-time browser approval as the bot user; thereafter the bot refreshes silently.
Migrate Matrix auth to appservice (MAS-durable)
2026-07-15 08:32:41 +00:00 · 2026-07-03 15:40:26 -07:00 · 2026-07-03 15:12:47 -07:00
7 changed files with 116 additions and 229 deletions
--- a/.env.example
+++ b/.env.example
@@ -1,7 +1,11 @@
 # ---- Matrix Connection ----
+# GogoBee authenticates as an appservice (MAS-durable). AS_TOKEN is the
+# as_token from registration.yaml — a Synapse-level credential that never
+# expires and is unaffected by Matrix Authentication Service. See
+# registration.yaml.example for the homeserver-side setup.
 HOMESERVER_URL=https://matrix.example.com
 BOT_USER_ID=@gogobee:example.com
-BOT_PASSWORD=your_password_here
+AS_TOKEN=your_appservice_as_token_here
 BOT_DISPLAY_NAME=GogoBee

 # Which rooms the bot posts scheduled content to (comma-separated room IDs)
--- a/README.md
+++ b/README.md
@@ -91,7 +91,14 @@ Everything is configured through environment variables or a `.env` file.
 |----------|-------------|
 | `HOMESERVER_URL` | Matrix homeserver URL, e.g. `https://matrix.org` |
 | `BOT_USER_ID` | Bot's Matrix user ID, e.g. `@gogobee:matrix.org` |
-| `BOT_PASSWORD` | Bot's Matrix password |
+| `AS_TOKEN` | Appservice `as_token` from `registration.yaml` (see below) |
+
+GogoBee authenticates as a Matrix **application service** rather than with a
+password. The `as_token` is a homeserver-level credential that never expires and
+is unaffected by Matrix Authentication Service (MAS) removing password login and
+UIA. Device E2EE keys are created via MSC4190. See
+[`registration.yaml.example`](registration.yaml.example) for the homeserver-side
+setup (register the appservice, enable `msc4190_enabled`, then set `AS_TOKEN`).

 ### Core (optional)

--- a/go.mod
+++ b/go.mod
@@ -13,7 +13,7 @@ require (
 	github.com/robfig/cron/v3 v3.0.1
 	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e
 	golang.org/x/image v0.40.0
-	maunium.net/go/mautrix v0.28.0
+	maunium.net/go/mautrix v0.28.1
 	modernc.org/sqlite v1.50.1
 )

@@ -25,7 +25,7 @@ require (
 	github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
-	github.com/mattn/go-sqlite3 v1.14.44 // indirect
+	github.com/mattn/go-sqlite3 v1.14.45 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect
 	github.com/petermattis/goid v0.0.0-20260330135022-df67b199bc81 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
@@ -35,12 +35,12 @@ require (
 	github.com/tidwall/match v1.1.1 // indirect
 	github.com/tidwall/pretty v1.2.1 // indirect
 	github.com/tidwall/sjson v1.2.5 // indirect
-	go.mau.fi/util v0.9.9 // indirect
-	golang.org/x/crypto v0.51.0 // indirect
-	golang.org/x/exp v0.0.0-20260508232706-74f9aab9d74a // indirect
-	golang.org/x/net v0.54.0 // indirect
-	golang.org/x/sys v0.44.0 // indirect
-	golang.org/x/text v0.37.0 // indirect
+	go.mau.fi/util v0.9.10 // indirect
+	golang.org/x/crypto v0.53.0 // indirect
+	golang.org/x/exp v0.0.0-20260611194520-c48552f49976 // indirect
+	golang.org/x/net v0.56.0 // indirect
+	golang.org/x/sys v0.46.0 // indirect
+	golang.org/x/text v0.38.0 // indirect
 	modernc.org/libc v1.72.3 // indirect
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.11.0 // indirect
--- a/go.sum
+++ b/go.sum
@@ -38,6 +38,8 @@ github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWE
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/mattn/go-sqlite3 v1.14.44 h1:3VSe+xafpbzsLbdr2AWlAZk9yRHiBhTBakioXaCKTF8=
 github.com/mattn/go-sqlite3 v1.14.44/go.mod h1:pjEuOr8IwzLJP2MfGeTb0A35jauH+C2kbHKBr7yXKVQ=
+github.com/mattn/go-sqlite3 v1.14.45 h1:6KA/spDguL3KV8rnybG7ezSaE4SeMR3KC9VbUoAQaIk=
+github.com/mattn/go-sqlite3 v1.14.45/go.mod h1:pjEuOr8IwzLJP2MfGeTb0A35jauH+C2kbHKBr7yXKVQ=
 github.com/ncruces/go-strftime v1.0.0 h1:HMFp8mLCTPp341M/ZnA4qaf7ZlsbTc+miZjCLOFAw7w=
 github.com/ncruces/go-strftime v1.0.0/go.mod h1:Fwc5htZGVVkseilnfgOVb9mKy6w1naJmn9CehxcKcls=
 github.com/notnil/joker v0.0.0-20180219043703-3f2f69a75914 h1:xXPuFr3PVM4p6Vw3j0CP29oWYRVKO3cPZjR6D7BxggQ=
@@ -75,6 +77,8 @@ github.com/tidwall/sjson v1.2.5/go.mod h1:Fvgq9kS/6ociJEDnK0Fk1cpYF4FIW6ZF7LAe+6
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 go.mau.fi/util v0.9.9 h1:ujDeXCo07HBor5oQLyO1tHklupmqVmPgasc53d7q/NE=
 go.mau.fi/util v0.9.9/go.mod h1:pqt4Vcrt+5gcH/CgrHZg11qSx+b34o6mknGzOEA6waY=
+go.mau.fi/util v0.9.10 h1:wzvz5iDHyqDXB8vgisD4d3SzucLXNM3iNY+1O1RoHtg=
+go.mau.fi/util v0.9.10/go.mod h1:YQOxySn+ZE3qSYqNxvyX7Yi3suA8YK17PS6QqBREW7A=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.13.0/go.mod h1:y6Z2r+Rw4iayiXXAIxJIDAJ1zMW4yaTpebo8fPOliYc=
@@ -83,8 +87,12 @@ golang.org/x/crypto v0.23.0/go.mod h1:CKFgDieR+mRhux2Lsu27y0fO304Db0wZe70UKqHu0v
 golang.org/x/crypto v0.31.0/go.mod h1:kDsLvtWBEx7MV9tJOj9bnXsPbxwJQ6csT/x4KIN4Ssk=
 golang.org/x/crypto v0.51.0 h1:IBPXwPfKxY7cWQZ38ZCIRPI50YLeevDLlLnyC5wRGTI=
 golang.org/x/crypto v0.51.0/go.mod h1:8AdwkbraGNABw2kOX6YFPs3WM22XqI4EXEd8g+x7Oc8=
+golang.org/x/crypto v0.53.0 h1:QZ4Muo8THX6CizN2vPPd5fBGHyogrdK9fG4wLPFUsto=
+golang.org/x/crypto v0.53.0/go.mod h1:DNLU434OwVakk9PzuwV8w62mAJpRJL3vsgcfp4Qnsio=
 golang.org/x/exp v0.0.0-20260508232706-74f9aab9d74a h1:+3jdDGGB8NGb1Zktc737jlt3/A5f6UlwSzmvqUuufxw=
 golang.org/x/exp v0.0.0-20260508232706-74f9aab9d74a/go.mod h1:d2fgXJLVs4dYDHUk5lwMIfzRzSrWCfGZb0ZqeLa/Vcw=
+golang.org/x/exp v0.0.0-20260611194520-c48552f49976 h1:X8Hz2ImujgbmetVuW+w2YkyZChE3cBpZi2P158rTG9M=
+golang.org/x/exp v0.0.0-20260611194520-c48552f49976/go.mod h1:vnf4pv9iKZXY58sQE1L86zmNWJ4159e1RkcWiLCkeEY=
 golang.org/x/image v0.40.0 h1:Tw4GyDXMo+daZN1znreBRC3VayR1aLFUyUEOLUdW1a8=
 golang.org/x/image v0.40.0/go.mod h1:uIc348UZMSvS5Z65CVZ7iDPaNobNFEPeJ4kbqTOszmA=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
@@ -94,6 +102,7 @@ golang.org/x/mod v0.15.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
 golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
 golang.org/x/mod v0.36.0 h1:JJjpVx6myfUsUdAzZuOSTTmRE0PfZeNWzzvKrP7amb4=
 golang.org/x/mod v0.36.0/go.mod h1:moc6ELqsWcOw5Ef3xVprK5ul/MvtVvkIXLziUOICjUQ=
+golang.org/x/mod v0.37.0 h1:vF1DjpVEshcIqoEaauuHebaLk1O1forxjxBaVn884JQ=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
@@ -105,6 +114,8 @@ golang.org/x/net v0.25.0/go.mod h1:JkAGAh7GEvH74S6FOH42FLoXpXbE/aqXSrIQjXgsiwM=
 golang.org/x/net v0.33.0/go.mod h1:HXLR5J+9DxmrqMwG9qjGCxZ+zKXxBru04zlTvWlWuN4=
 golang.org/x/net v0.54.0 h1:2zJIZAxAHV/OHCDTCOHAYehQzLfSXuf/5SoL/Dv6w/w=
 golang.org/x/net v0.54.0/go.mod h1:Sj4oj8jK6XmHpBZU/zWHw3BV3abl4Kvi+Ut7cQcY+cQ=
+golang.org/x/net v0.56.0 h1:Rw8j/hFzGvJUZwNBXnAtf5sVDVt+65SK2C7IxCxZt5o=
+golang.org/x/net v0.56.0/go.mod h1:D3Ku6r+V6JROoZK144D2XfMHFcMq/0zSfLelVTCFKec=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -114,6 +125,7 @@ golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sync v0.10.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
 golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sync v0.21.0 h1:HLII4xRRTtCRkxYp4HNFF0Js/Og6q2i++KXbg0gHCwM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
@@ -128,6 +140,8 @@ golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.28.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.44.0 h1:ildZl3J4uzeKP07r2F++Op7E9B29JRUy+a27EibtBTQ=
 golang.org/x/sys v0.44.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/sys v0.46.0 h1:noSf2Fq6F8DBgS+LysIkx7rIExoNHJsxOAtPp4rthXw=
+golang.org/x/sys v0.46.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
 golang.org/x/telemetry v0.0.0-20240228155512-f48c80bd79b2/go.mod h1:TeRTkGYfJXctD9OcfyVLyj2J3IxLnKwHJR8f4D8a3YE=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
@@ -148,6 +162,8 @@ golang.org/x/text v0.15.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
 golang.org/x/text v0.21.0/go.mod h1:4IBbMaMmOPCJ8SecivzSH54+73PCFmPWxNTLm+vZkEQ=
 golang.org/x/text v0.37.0 h1:Cqjiwd9eSg8e0QAkyCaQTNHFIIzWtidPahFWR83rTrc=
 golang.org/x/text v0.37.0/go.mod h1:a5sjxXGs9hsn/AJVwuElvCAo9v8QYLzvavO5z2PiM38=
+golang.org/x/text v0.38.0 h1:sXmwo9DwP3OK9EZ7PqAdaooSGozfl/3a6/xJcbzPRhE=
+golang.org/x/text v0.38.0/go.mod h1:YXZt3QhHUKYT53r2lLKFIVi6Ao1jdzrTR/KQ09qyxF4=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
@@ -156,6 +172,7 @@ golang.org/x/tools v0.13.0/go.mod h1:HvlwmtVNQAhOuCjW7xxvovg8wbNq7LwfXh/k7wXUl58
 golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
 golang.org/x/tools v0.45.0 h1:18qN3FAooORvApf5XjCXgsuayZOEtXf6JK18I3+ONa8=
 golang.org/x/tools v0.45.0/go.mod h1:LuUGqqaXcXMEFEruIVJVm5mgDD8vww/z/SR1gQ4uE/0=
+golang.org/x/tools v0.46.0 h1:7jTurBkPZu4moS/Uy4OQT1M+QBlsj3wejyZwsT8Z7rk=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
@@ -163,6 +180,8 @@ gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 maunium.net/go/mautrix v0.28.0 h1:vBakLzf8MAdfED3NzAKiMeKQbc3AQ4EAS03NC+TVMXQ=
 maunium.net/go/mautrix v0.28.0/go.mod h1:/a9A7LGaqb9B3nho4tLd28n0EPcCdwpm2dxkxkLLgh0=
+maunium.net/go/mautrix v0.28.1 h1:Hic3oDMPbLbQu1fhboTRAKZcORMjzzkjxsa+SGk60b0=
+maunium.net/go/mautrix v0.28.1/go.mod h1:mWXQNmOlrq4VTDU9f1HO03BSIswdUIyyY4wUKHqwzzY=
 modernc.org/cc/v4 v4.28.2 h1:3tQ0lf2ADtoby2EtSP+J7IE2SHwEJdP8ioR59wx7XpY=
 modernc.org/cc/v4 v4.28.2/go.mod h1:OnovgIhbbMXMu1aISnJ0wvVD1KnW+cAUJkIrAWh+kVI=
 modernc.org/ccgo/v4 v4.34.0 h1:yRLPFZieg532OT4rp4JFNIVcquwalMX26G95WQDqwCQ=
--- a/internal/bot/client.go
+++ b/internal/bot/client.go
@@ -2,203 +2,146 @@ package bot

 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"log/slog"
 	"os"
 	"path/filepath"

-	"gogobee/internal/util"
-
 	"maunium.net/go/mautrix"
 	"maunium.net/go/mautrix/crypto/cryptohelper"
 	"maunium.net/go/mautrix/id"
 )

-// DeviceInfo holds persisted device credentials.
-type DeviceInfo struct {
-	AccessToken string `json:"access_token"`
-	DeviceID    string `json:"device_id"`
-	UserID      string `json:"user_id"`
-}
-
 // Config holds the bot's startup configuration.
 type Config struct {
 	Homeserver  string
-	UserID      string
-	Password    string
+	UserID      string // Bot's full Matrix user ID, e.g. @gogobee:example.com
+	ASToken     string // Appservice as_token from registration.yaml
 	DataDir     string
 	DisplayName string
 }

-// NewClient creates and configures a mautrix client with E2EE support.
-// The cryptohelper handles:
-//   - Persistent crypto store in SQLite (device keys, sessions, cross-signing keys)
-//   - Automatic cross-signing bootstrap (self-signs the device on first run)
-//   - Automatic device trust via cross-signing (no manual verification needed)
-//   - Megolm session sharing and key exchange
-//   - Olm session management for device-to-device encryption
+// NewClient creates and configures a mautrix client authenticated as an
+// application service, with E2EE via the cryptohelper.
 //
-// This solves the TS version's device verification issues because:
-//   1. Crypto state persists across restarts (not in-memory like fake-indexeddb)
-//   2. Cross-signing makes other devices trust this bot automatically
-//   3. The bot trusts all users' devices by default (appropriate for a bot)
-//   4. No manual emoji/SAS verification needed
+// Why appservice instead of password login:
+//
+// Under Matrix Authentication Service (MAS), the legacy password login
+// (m.login.password) and User-Interactive Auth (UIA) flows are being removed —
+// auth moves to OAuth2/OIDC. A bot built on password login + password-UIA
+// cross-signing (the old code) breaks in a MAS world: short-lived tokens with
+// no refresh, and UIA-gated key uploads that simply fail.
+//
+// The appservice model sidesteps MAS entirely. The as_token is a Synapse-level
+// trust relationship declared in registration.yaml — Synapse validates it
+// directly, not via MAS — so it never expires and needs no login flow. Device
+// creation uses MSC4190 (PUT /devices), which replaces the UIA-gated device
+// dance for appservice users. This is the MAS-durable path.
+//
+// The cryptohelper still handles everything E2EE:
+//   - Persistent crypto store in SQLite (device keys, sessions, cross-signing)
+//   - Megolm session sharing / key exchange, Olm device-to-device sessions
+//   - The bot trusts all users' devices by default (appropriate for a bot)
+//   - No interactive emoji/SAS verification needed
 func NewClient(cfg Config) (*mautrix.Client, error) {
 	if err := os.MkdirAll(cfg.DataDir, 0o755); err != nil {
 		return nil, fmt.Errorf("create data dir: %w", err)
 	}
+	if cfg.ASToken == "" {
+		return nil, fmt.Errorf("AS_TOKEN is required (appservice registration as_token)")
+	}
+	if cfg.UserID == "" {
+		return nil, fmt.Errorf("BOT_USER_ID is required")
+	}

-	devicePath := filepath.Join(cfg.DataDir, "device.json")
+	ctx := context.Background()
+	userID := id.UserID(cfg.UserID)

-	// Try to load existing device credentials
-	device, err := loadDevice(devicePath)
+	// The as_token IS the access token. No login flow, no refresh — Synapse
+	// trusts it for any user in the registration's namespace.
+	client, err := mautrix.NewClient(cfg.Homeserver, userID, cfg.ASToken)
 	if err != nil {
-		slog.Info("no existing device found, will login fresh")
+		return nil, fmt.Errorf("create client: %w", err)
 	}

-	var client *mautrix.Client
+	// Assert our own user ID on every request (appservice identity assertion,
+	// ?user_id=). Required so Synapse knows which namespaced user we're acting
+	// as — including on /sync and the MSC4190 device creation below.
+	client.SetAppServiceUserID = true

-	if device != nil {
-		// Validate existing token
-		valid, _ := util.IsTokenValid(cfg.Homeserver, device.AccessToken)
-		if valid {
-			slog.Info("existing device credentials valid", "device_id", device.DeviceID)
-			userID := id.UserID(device.UserID)
-			client, err = mautrix.NewClient(cfg.Homeserver, userID, device.AccessToken)
-			if err != nil {
-				return nil, fmt.Errorf("create client with existing token: %w", err)
-			}
-			client.DeviceID = id.DeviceID(device.DeviceID)
-		} else {
-			slog.Warn("existing device credentials invalid, logging in again")
-			device = nil
-		}
+	// Validate the token + homeserver reachability up front with a clear error.
+	whoami, err := client.Whoami(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("appservice token validation failed (whoami): %w", err)
 	}
-
-	if device == nil {
-		// Fresh login
-		loginResp, err := util.LoginWithPassword(cfg.Homeserver, cfg.UserID, cfg.Password, cfg.DisplayName)
-		if err != nil {
-			return nil, fmt.Errorf("login: %w", err)
-		}
-
-		userID := id.UserID(loginResp.UserID)
-		client, err = mautrix.NewClient(cfg.Homeserver, userID, loginResp.AccessToken)
-		if err != nil {
-			return nil, fmt.Errorf("create client: %w", err)
-		}
-		client.DeviceID = id.DeviceID(loginResp.DeviceID)
-
-		// Save device info
-		device = &DeviceInfo{
-			AccessToken: loginResp.AccessToken,
-			DeviceID:    loginResp.DeviceID,
-			UserID:      loginResp.UserID,
-		}
-		if err := saveDevice(devicePath, device); err != nil {
-			slog.Warn("failed to save device info", "err", err)
-		}
-
-		slog.Info("logged in successfully",
-			"user_id", loginResp.UserID,
-			"device_id", loginResp.DeviceID,
-		)
+	if whoami.UserID != userID {
+		return nil, fmt.Errorf("appservice identity mismatch: token resolves to %s but BOT_USER_ID is %s", whoami.UserID, userID)
 	}
+	slog.Info("appservice token valid", "user_id", whoami.UserID)

-	// Set up E2EE via cryptohelper — stores crypto state in its own SQLite DB,
-	// separate from the main app database. Unlike the TS version which used an
-	// in-memory fake-indexeddb store that was lost on restart (causing constant
-	// re-verification), mautrix-go's cryptohelper persists everything in SQLite:
-	// device keys, olm/megolm sessions, cross-signing keys, and device trust state.
-	//
-	// We pass just the raw file path — the cryptohelper wraps it in a file: URI
-	// with _txlock=immediate internally (see cryptohelper.go line 82).
+	// Set up E2EE. The cryptohelper persists all crypto state in its own SQLite
+	// DB (device keys, olm/megolm sessions, cross-signing keys, device trust),
+	// separate from the main app database. The device ID is persisted there too,
+	// so restarts reuse the same device — no device.json needed.
 	cryptoDBPath := filepath.Join(cfg.DataDir, "crypto.db")
 	ch, err := cryptohelper.NewCryptoHelper(client, []byte("gogobee_pickle_key"), cryptoDBPath)
 	if err != nil {
 		return nil, fmt.Errorf("init crypto helper: %w", err)
 	}

-	// LoginAs enables the cryptohelper to re-login if the token expires,
-	// and to bootstrap cross-signing on first run. Cross-signing means:
-	//   - The bot's master key signs its own device key
-	//   - Other users/devices that have verified the bot's master key
-	//     will automatically trust this device
-	//   - No interactive emoji/SAS verification needed
+	// MSC4190: create/refresh the bot's device via PUT /devices instead of the
+	// UIA-gated login dance. On first run the crypto store has no device ID, so
+	// a fresh one is generated and persisted; on restart the stored ID is
+	// reused (the PUT is idempotent). LoginAs carries only the display name —
+	// in MSC4190 mode the cryptohelper never calls /login.
+	ch.MSC4190 = true
 	ch.LoginAs = &mautrix.ReqLogin{
-		Type: mautrix.AuthTypePassword,
-		Identifier: mautrix.UserIdentifier{
-			Type: mautrix.IdentifierTypeUser,
-			User: cfg.UserID,
-		},
-		Password:                 cfg.Password,
 		InitialDeviceDisplayName: cfg.DisplayName,
 	}

-	if err := ch.Init(context.Background()); err != nil {
-		return nil, fmt.Errorf("crypto helper init: %w", err)
+	if err := ch.Init(ctx); err != nil {
+		return nil, fmt.Errorf("crypto helper init (MSC4190 device create): %w", err)
 	}
-
-	// Attach crypto helper to client
 	client.Crypto = ch

-	// Bootstrap cross-signing: generate keys, sign own device, sign master key.
-	// This makes the bot's device show as "verified" to other users.
+	// Best-effort cross-signing bootstrap. This makes the bot's device show as
+	// "verified" to users who have verified the bot's master key. It is NOT
+	// required for E2EE to function — the bot already trusts all devices and
+	// shares keys — so any failure is logged and ignored.
+	//
+	// Under MSC3202 (appservice device assertion) Synapse may accept the key
+	// upload without UIA, in which case the callback below is never invoked. If
+	// the homeserver still demands UIA, we have no password credential to
+	// satisfy it (that's the whole point of going MAS-native), so it fails soft.
 	mach := ch.Machine()
-	recoveryKey, _, err := mach.GenerateAndUploadCrossSigningKeys(context.Background(), func(ui *mautrix.RespUserInteractive) interface{} {
-		return map[string]interface{}{
-			"type": mautrix.AuthTypePassword,
-			"identifier": map[string]interface{}{
-				"type": mautrix.IdentifierTypeUser,
-				"user": cfg.UserID,
-			},
-			"password": cfg.Password,
-			"session":  ui.Session,
-		}
+	recoveryKey, _, err := mach.GenerateAndUploadCrossSigningKeys(ctx, func(ui *mautrix.RespUserInteractive) interface{} {
+		slog.Warn("cross-signing: homeserver requested UIA, but appservice auth has no password credential to satisfy it — skipping verified-shield bootstrap")
+		return map[string]interface{}{"session": ui.Session}
 	}, "")
 	if err != nil {
-		slog.Warn("cross-signing: key upload failed (may already exist)", "err", err)
+		slog.Warn("cross-signing: key upload skipped (may already exist or UIA required)", "err", err)
 	} else {
 		slog.Info("cross-signing: keys uploaded", "recovery_key", recoveryKey)
 	}

-	if err := mach.SignOwnDevice(context.Background(), mach.OwnIdentity()); err != nil {
+	if err := mach.SignOwnDevice(ctx, mach.OwnIdentity()); err != nil {
 		slog.Warn("cross-signing: sign own device failed", "err", err)
 	} else {
 		slog.Info("cross-signing: own device signed")
 	}

-	if err := mach.SignOwnMasterKey(context.Background()); err != nil {
+	if err := mach.SignOwnMasterKey(ctx); err != nil {
 		slog.Warn("cross-signing: sign master key failed", "err", err)
 	} else {
 		slog.Info("cross-signing: master key signed")
 	}

 	slog.Info("E2EE initialized",
+		"user_id", client.UserID,
 		"device_id", client.DeviceID,
 		"crypto_store", "sqlite-persistent",
+		"auth", "appservice+msc4190",
 	)

 	return client, nil
 }
-
-func loadDevice(path string) (*DeviceInfo, error) {
-	data, err := os.ReadFile(path)
-	if err != nil {
-		return nil, err
-	}
-	var info DeviceInfo
-	if err := json.Unmarshal(data, &info); err != nil {
-		return nil, err
-	}
-	return &info, nil
-}
-
-func saveDevice(path string, info *DeviceInfo) error {
-	data, err := json.MarshalIndent(info, "", "  ")
-	if err != nil {
-		return err
-	}
-	return os.WriteFile(path, data, 0o600)
-}
--- a/internal/util/auth.go
+++ b/internal/util/auth.go
@@ -1,86 +0,0 @@
-package util
-
-import (
-	"bytes"
-	"encoding/json"
-	"fmt"
-	"io"
-	"net/http"
-	"time"
-)
-
-// LoginResponse holds the Matrix login response fields we care about.
-type LoginResponse struct {
-	AccessToken string `json:"access_token"`
-	DeviceID    string `json:"device_id"`
-	UserID      string `json:"user_id"`
-}
-
-// LoginWithPassword performs a Matrix password login.
-func LoginWithPassword(homeserver, user, password, deviceDisplayName string) (*LoginResponse, error) {
-	url := homeserver + "/_matrix/client/v3/login"
-
-	body := map[string]any{
-		"type": "m.login.password",
-		"identifier": map[string]string{
-			"type": "m.id.user",
-			"user": user,
-		},
-		"password":                password,
-		"initial_device_display_name": deviceDisplayName,
-	}
-
-	data, err := json.Marshal(body)
-	if err != nil {
-		return nil, fmt.Errorf("marshal login body: %w", err)
-	}
-
-	client := &http.Client{Timeout: 30 * time.Second}
-	resp, err := client.Post(url, "application/json", bytes.NewReader(data))
-	if err != nil {
-		return nil, fmt.Errorf("login request: %w", err)
-	}
-	defer resp.Body.Close()
-
-	respBody, _ := io.ReadAll(resp.Body)
-	if resp.StatusCode != 200 {
-		return nil, fmt.Errorf("login failed (HTTP %d): %s", resp.StatusCode, string(respBody))
-	}
-
-	var result LoginResponse
-	if err := json.Unmarshal(respBody, &result); err != nil {
-		return nil, fmt.Errorf("parse login response: %w", err)
-	}
-	return &result, nil
-}
-
-// IsTokenValid checks if an access token is still valid via /account/whoami.
-func IsTokenValid(homeserver, accessToken string) (bool, string) {
-	url := homeserver + "/_matrix/client/v3/account/whoami"
-
-	req, err := http.NewRequest("GET", url, nil)
-	if err != nil {
-		return false, ""
-	}
-	req.Header.Set("Authorization", "Bearer "+accessToken)
-
-	client := &http.Client{Timeout: 10 * time.Second}
-	resp, err := client.Do(req)
-	if err != nil {
-		return false, ""
-	}
-	defer resp.Body.Close()
-
-	if resp.StatusCode != 200 {
-		return false, ""
-	}
-
-	var result struct {
-		UserID string `json:"user_id"`
-	}
-	body, _ := io.ReadAll(resp.Body)
-	if err := json.Unmarshal(body, &result); err != nil {
-		return false, ""
-	}
-	return true, result.UserID
-}
--- a/main.go
+++ b/main.go
@@ -59,7 +59,7 @@ func main() {
 	cfg := bot.Config{
 		Homeserver:  os.Getenv("HOMESERVER_URL"),
 		UserID:      os.Getenv("BOT_USER_ID"),
-		Password:    os.Getenv("BOT_PASSWORD"),
+		ASToken:     os.Getenv("AS_TOKEN"),
 		DataDir:     dataDir,
 		DisplayName: envOr("BOT_DISPLAY_NAME", "GogoBee"),
 	}