MM-23935 extend session expiry on user activity (#14275)

* MM-23935  extend session expiry on user activity

- if user types anything before a session expires the session will be extended to now + session length

- ensures new session expiries are not written to DB too frequently

- new session store func for updating session ExpiresAt

- session length defaults for mobile and web/ldap changed from 180 days to 30 days

app/app_iface.go

@@ -121,6 +121,10 @@ type AppIface interface {
 	// attributes of the attachment structure. The Slack attachment structure is
 	// documented here: https://api.slack.com/docs/attachments
 	ProcessSlackAttachments(attachments []*model.SlackAttachment) []*model.SlackAttachment
+	// ExtendSessionExpiryIfNeeded extends Session.ExpiresAt based on session lengths in config.
+	// A new ExpiresAt is only written if enough time has elapsed since last update.
+	// Returns true only if the session was extended.
+	ExtendSessionExpiryIfNeeded(session *model.Session) bool
 	// FillInPostProps should be invoked before saving posts to fill in properties such as
 	// channel_mentions.
 	//
@@ -183,6 +187,9 @@ type AppIface interface {
 	GetSanitizedConfig() *model.Config
 	// GetSchemeRolesForChannel Checks if a channel or its team has an override scheme for channel roles and returns the scheme roles or default channel roles.
 	GetSchemeRolesForChannel(channelId string) (guestRoleName string, userRoleName string, adminRoleName string, err *model.AppError)
+	// GetSessionLengthInMillis returns the session length, in milliseconds,
+	// based on the type of session (Mobile, SSO, Web/LDAP).
+	GetSessionLengthInMillis(session *model.Session) int64
 	// GetTeamGroupUsers returns the users who are associated to the team via GroupTeams and GroupMembers.
 	GetTeamGroupUsers(teamID string) ([]*model.User, *model.AppError)
 	// GetTeamSchemeChannelRoles Checks if a team has an override scheme and returns the scheme channel role names or default channel role names.