feat: admin APIs for token authenticated registration (#3101)

### Pull Request Checklist

<!-- Please read
https://matrix-org.github.io/dendrite/development/contributing before
submitting your pull request -->

* [x] I have added Go unit tests or [Complement integration
tests](https://github.com/matrix-org/complement) for this PR _or_ I have
justified why this PR doesn't need tests
* [x] Pull request includes a [sign off below using a legally
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_or_ I have already signed off privately

Signed-off-by: `Santhoshivan Amudhan santhoshivan23@gmail.com`

2 files changed, 272 insertions, 0 deletions

diff --git a/clientapi/routing/admin.go b/clientapi/routing/admin.go
index 3d64454c..51966607 100644
--- a/clientapi/routing/admin.go
+++ b/clientapi/routing/admin.go
@@ -6,6 +6,8 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"regexp"
+	"strconv"
 	"time"
 
 	"github.com/gorilla/mux"
@@ -16,14 +18,254 @@ import (
 	"github.com/matrix-org/util"
 	"github.com/nats-io/nats.go"
 	"github.com/sirupsen/logrus"
+	"golang.org/x/exp/constraints"
 
+	clientapi "github.com/matrix-org/dendrite/clientapi/api"
 	"github.com/matrix-org/dendrite/internal/httputil"
 	roomserverAPI "github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dendrite/setup/jetstream"
 	"github.com/matrix-org/dendrite/userapi/api"
+	userapi "github.com/matrix-org/dendrite/userapi/api"
 )
 
+var validRegistrationTokenRegex = regexp.MustCompile("^[[:ascii:][:digit:]_]*$")
+
+func AdminCreateNewRegistrationToken(req *http.Request, cfg *config.ClientAPI, userAPI userapi.ClientUserAPI) util.JSONResponse {
+	if !cfg.RegistrationRequiresToken {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden("Registration via tokens is not enabled on this homeserver"),
+		}
+	}
+	request := struct {
+		Token       string `json:"token"`
+		UsesAllowed *int32 `json:"uses_allowed,omitempty"`
+		ExpiryTime  *int64 `json:"expiry_time,omitempty"`
+		Length      int32  `json:"length"`
+	}{}
+
+	if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.BadJSON(fmt.Sprintf("Failed to decode request body: %s", err)),
+		}
+	}
+
+	token := request.Token
+	usesAllowed := request.UsesAllowed
+	expiryTime := request.ExpiryTime
+	length := request.Length
+
+	if len(token) == 0 {
+		if length == 0 {
+			// length not provided in request. Assign default value of 16.
+			length = 16
+		}
+		// token not present in request body. Hence, generate a random token.
+		if length <= 0 || length > 64 {
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: spec.BadJSON("length must be greater than zero and not greater than 64"),
+			}
+		}
+		token = util.RandomString(int(length))
+	}
+
+	if len(token) > 64 {
+		//Token present in request body, but is too long.
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.BadJSON("token must not be longer than 64"),
+		}
+	}
+
+	isTokenValid := validRegistrationTokenRegex.Match([]byte(token))
+	if !isTokenValid {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.BadJSON("token must consist only of characters matched by the regex [A-Za-z0-9-_]"),
+		}
+	}
+	// At this point, we have a valid token, either through request body or through random generation.
+	if usesAllowed != nil && *usesAllowed < 0 {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.BadJSON("uses_allowed must be a non-negative integer or null"),
+		}
+	}
+	if expiryTime != nil && spec.Timestamp(*expiryTime).Time().Before(time.Now()) {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.BadJSON("expiry_time must not be in the past"),
+		}
+	}
+	pending := int32(0)
+	completed := int32(0)
+	// If usesAllowed or expiryTime is 0, it means they are not present in the request. NULL (indicating unlimited uses / no expiration will be persisted in DB)
+	registrationToken := &clientapi.RegistrationToken{
+		Token:       &token,
+		UsesAllowed: usesAllowed,
+		Pending:     &pending,
+		Completed:   &completed,
+		ExpiryTime:  expiryTime,
+	}
+	created, err := userAPI.PerformAdminCreateRegistrationToken(req.Context(), registrationToken)
+	if !created {
+		return util.JSONResponse{
+			Code: http.StatusConflict,
+			JSON: map[string]string{
+				"error": fmt.Sprintf("token: %s already exists", token),
+			},
+		}
+	}
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: err,
+		}
+	}
+	return util.JSONResponse{
+		Code: 200,
+		JSON: map[string]interface{}{
+			"token":        token,
+			"uses_allowed": getReturnValue(usesAllowed),
+			"pending":      pending,
+			"completed":    completed,
+			"expiry_time":  getReturnValue(expiryTime),
+		},
+	}
+}
+
+func getReturnValue[t constraints.Integer](in *t) any {
+	if in == nil {
+		return nil
+	}
+	return *in
+}
+
+func AdminListRegistrationTokens(req *http.Request, cfg *config.ClientAPI, userAPI userapi.ClientUserAPI) util.JSONResponse {
+	queryParams := req.URL.Query()
+	returnAll := true
+	valid := true
+	validQuery, ok := queryParams["valid"]
+	if ok {
+		returnAll = false
+		validValue, err := strconv.ParseBool(validQuery[0])
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: spec.BadJSON("invalid 'valid' query parameter"),
+			}
+		}
+		valid = validValue
+	}
+	tokens, err := userAPI.PerformAdminListRegistrationTokens(req.Context(), returnAll, valid)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.ErrorUnknown,
+		}
+	}
+	return util.JSONResponse{
+		Code: 200,
+		JSON: map[string]interface{}{
+			"registration_tokens": tokens,
+		},
+	}
+}
+
+func AdminGetRegistrationToken(req *http.Request, cfg *config.ClientAPI, userAPI userapi.ClientUserAPI) util.JSONResponse {
+	vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
+	if err != nil {
+		return util.ErrorResponse(err)
+	}
+	tokenText := vars["token"]
+	token, err := userAPI.PerformAdminGetRegistrationToken(req.Context(), tokenText)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusNotFound,
+			JSON: spec.NotFound(fmt.Sprintf("token: %s not found", tokenText)),
+		}
+	}
+	return util.JSONResponse{
+		Code: 200,
+		JSON: token,
+	}
+}
+
+func AdminDeleteRegistrationToken(req *http.Request, cfg *config.ClientAPI, userAPI userapi.ClientUserAPI) util.JSONResponse {
+	vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
+	if err != nil {
+		return util.ErrorResponse(err)
+	}
+	tokenText := vars["token"]
+	err = userAPI.PerformAdminDeleteRegistrationToken(req.Context(), tokenText)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: err,
+		}
+	}
+	return util.JSONResponse{
+		Code: 200,
+		JSON: map[string]interface{}{},
+	}
+}
+
+func AdminUpdateRegistrationToken(req *http.Request, cfg *config.ClientAPI, userAPI userapi.ClientUserAPI) util.JSONResponse {
+	vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
+	if err != nil {
+		return util.ErrorResponse(err)
+	}
+	tokenText := vars["token"]
+	request := make(map[string]*int64)
+	if err = json.NewDecoder(req.Body).Decode(&request); err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.BadJSON(fmt.Sprintf("Failed to decode request body: %s", err)),
+		}
+	}
+	newAttributes := make(map[string]interface{})
+	usesAllowed, ok := request["uses_allowed"]
+	if ok {
+		// Only add usesAllowed to newAtrributes if it is present and valid
+		if usesAllowed != nil && *usesAllowed < 0 {
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: spec.BadJSON("uses_allowed must be a non-negative integer or null"),
+			}
+		}
+		newAttributes["usesAllowed"] = usesAllowed
+	}
+	expiryTime, ok := request["expiry_time"]
+	if ok {
+		// Only add expiryTime to newAtrributes if it is present and valid
+		if expiryTime != nil && spec.Timestamp(*expiryTime).Time().Before(time.Now()) {
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: spec.BadJSON("expiry_time must not be in the past"),
+			}
+		}
+		newAttributes["expiryTime"] = expiryTime
+	}
+	if len(newAttributes) == 0 {
+		// No attributes to update. Return existing token
+		return AdminGetRegistrationToken(req, cfg, userAPI)
+	}
+	updatedToken, err := userAPI.PerformAdminUpdateRegistrationToken(req.Context(), tokenText, newAttributes)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusNotFound,
+			JSON: spec.NotFound(fmt.Sprintf("token: %s not found", tokenText)),
+		}
+	}
+	return util.JSONResponse{
+		Code: 200,
+		JSON: *updatedToken,
+	}
+}
+
 func AdminEvacuateRoom(req *http.Request, rsAPI roomserverAPI.ClientRoomserverAPI) util.JSONResponse {
 	vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
 	if err != nil {
diff --git a/clientapi/routing/routing.go b/clientapi/routing/routing.go
index d3f19cae..ab4aefdd 100644
--- a/clientapi/routing/routing.go
+++ b/clientapi/routing/routing.go
@@ -162,6 +162,36 @@ func Setup(
 			}),
 		).Methods(http.MethodGet, http.MethodPost, http.MethodOptions)
 	}
+	dendriteAdminRouter.Handle("/admin/registrationTokens/new",
+		httputil.MakeAdminAPI("admin_registration_tokens_new", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			return AdminCreateNewRegistrationToken(req, cfg, userAPI)
+		}),
+	).Methods(http.MethodPost, http.MethodOptions)
+
+	dendriteAdminRouter.Handle("/admin/registrationTokens",
+		httputil.MakeAdminAPI("admin_list_registration_tokens", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			return AdminListRegistrationTokens(req, cfg, userAPI)
+		}),
+	).Methods(http.MethodGet, http.MethodOptions)
+
+	dendriteAdminRouter.Handle("/admin/registrationTokens/{token}",
+		httputil.MakeAdminAPI("admin_get_registration_token", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			switch req.Method {
+			case http.MethodGet:
+				return AdminGetRegistrationToken(req, cfg, userAPI)
+			case http.MethodPut:
+				return AdminUpdateRegistrationToken(req, cfg, userAPI)
+			case http.MethodDelete:
+				return AdminDeleteRegistrationToken(req, cfg, userAPI)
+			default:
+				return util.MatrixErrorResponse(
+					404,
+					string(spec.ErrorNotFound),
+					"unknown method",
+				)
+			}
+		}),
+	).Methods(http.MethodGet, http.MethodPut, http.MethodDelete, http.MethodOptions)
 
 	dendriteAdminRouter.Handle("/admin/evacuateRoom/{roomID}",
 		httputil.MakeAdminAPI("admin_evacuate_room", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {