Matrix: Setup bot, add PIN verification

PIN is verified but not used currently. Works a little different than
the others, you input your matrix user ID and then the PIN is sent to
you. The bot doesn't support E2EE, so the bot being the first one to
message ensures the chat is unencrypted.

api.go

@@ -2233,6 +2233,68 @@ func (app *appContext) DiscordServerInvite(gc *gin.Context) {
 	gc.JSON(200, DiscordInviteDTO{invURL, iconURL})
 }
 
+// @Summary Generate and send a new PIN to a specified Matrix user.
+// @Produce json
+// @Success 200 {object} boolResponse
+// @Failure 400 {object} boolResponse
+// @Failure 401 {object} boolResponse
+// @Failure 500 {object} boolResponse
+// @Param invCode path string true "invite Code"
+// @Param MatrixSendPINDTO body MatrixSendPINDTO true "User's Matrix ID."
+// @Router /invite/{invCode}/matrix/user [post]
+// @tags Other
+func (app *appContext) MatrixSendPIN(gc *gin.Context) {
+	code := gc.Param("invCode")
+	if _, ok := app.storage.invites[code]; !ok {
+		respondBool(401, false, gc)
+		return
+	}
+	var req MatrixSendPINDTO
+	gc.BindJSON(&req)
+	if req.UserID == "" {
+		respondBool(400, false, gc)
+		return
+	}
+	ok := app.matrix.SendStart(req.UserID)
+	if !ok {
+		respondBool(500, false, gc)
+		return
+	}
+	respondBool(200, true, gc)
+}
+
+// @Summary Check whether a matrix PIN is valid. Requires invite code.
+// @Produce json
+// @Success 200 {object} boolResponse
+// @Failure 401 {object} boolResponse
+// @Param pin path string true "PIN code to check"
+// @Param invCode path string true "invite Code"
+// @Param userID path string true "Matrix User ID"
+// @Router /invite/{invCode}/matrix/verified/{userID}/{pin} [get]
+// @tags Other
+func (app *appContext) MatrixCheckPIN(gc *gin.Context) {
+	code := gc.Param("invCode")
+	if _, ok := app.storage.invites[code]; !ok {
+		app.debug.Println("Matrix: Invite code was invalid")
+		respondBool(401, false, gc)
+		return
+	}
+	userID := gc.Param("userID")
+	pin := gc.Param("pin")
+	user, ok := app.matrix.tokens[pin]
+	if !ok {
+		app.debug.Println("Matrix: PIN not found")
+		respondBool(200, false, gc)
+		return
+	}
+	if user.User.UserID != userID {
+		app.debug.Println("Matrix: User ID of PIN didn't match")
+		respondBool(200, false, gc)
+		return
+	}
+	respondBool(200, true, gc)
+}
+
 // @Summary Returns a list of matching users from a Discord guild, given a username (discriminator optional).
 // @Produce json
 // @Success 200 {object} DiscordUsersDTO