add basic oauth bounces

src/functions/bot-join/README.md

@@ -0,0 +1,10 @@
+# Bot Join Bounce Service
+
+This function sends a user to the necessary Discord.com Bot OAuth flow.
+
+Two cases may be present:
+
+- General: The user will be sent to allow any of their relevant servers to join
+  - This flow would be triggered from a generalized button
+- Specific: The user will be sent to join one of their servers.
+  - This flow would be triggered from server picker

src/functions/bot-join/botjoin.go

@@ -0,0 +1,45 @@
+package botjoin
+
+import (
+	"bytes"
+	"net/http"
+	"regexp"
+	"text/template"
+
+	"github.com/roleypoly/roleypoly/src/common"
+	"github.com/roleypoly/roleypoly/src/common/faas"
+)
+
+var (
+	validGuildID         = regexp.MustCompile(`^[0-9]+$`)
+	redirectPathTemplate = template.Must(
+		template.New("redirect").Parse(
+			`https://discord.com/api/oauth2/authorize?client_id={{.ClientID}}&scope=bot&permissions={{.Permissions}}{{if .GuildID}}&guild_id={{.GuildID}}&disable_guild_select=true{{end}}`,
+		),
+	)
+	clientID = common.Getenv("BOT_CLIENT_ID").String()
+)
+
+type redirectPathData struct {
+	ClientID    string
+	Permissions int
+	GuildID     string
+}
+
+func BotJoin(rw http.ResponseWriter, r *http.Request) {
+	guildID := r.URL.Query().Get("guild")
+	if !validGuildID.MatchString(guildID) {
+		guildID = ""
+	}
+
+	pathData := redirectPathData{
+		ClientID:    clientID,
+		Permissions: 268435456, // MANAGE_ROLES
+		GuildID:     guildID,
+	}
+
+	pathBuffer := bytes.Buffer{}
+	redirectPathTemplate.Execute(&pathBuffer, pathData)
+
+	faas.Bounce(rw, pathBuffer.String())
+}

src/functions/bot-join/botjoin_test.go

@@ -0,0 +1,36 @@
+package botjoin_test
+
+import (
+	"net/http/httptest"
+	"testing"
+
+	"github.com/onsi/gomega"
+	botjoin "github.com/roleypoly/roleypoly/src/functions/bot-join"
+)
+
+func TestGeneral(t *testing.T) {
+	O := gomega.NewWithT(t)
+
+	req := httptest.NewRequest("GET", "/bot-join", nil)
+	resp := httptest.NewRecorder()
+
+	botjoin.BotJoin(resp, req)
+
+	result := resp.Result()
+	O.Expect(result.StatusCode).Should(gomega.BeIdenticalTo(303))
+	O.Expect(result.Header.Get("location")).ShouldNot(gomega.ContainSubstring("guild_id"))
+
+}
+
+func TestGeneralSpecific(t *testing.T) {
+	O := gomega.NewWithT(t)
+
+	req := httptest.NewRequest("GET", "/bot-join?guild=386659935687147521", nil)
+	resp := httptest.NewRecorder()
+
+	botjoin.BotJoin(resp, req)
+
+	result := resp.Result()
+	O.Expect(result.StatusCode).Should(gomega.BeIdenticalTo(303))
+	O.Expect(result.Header.Get("location")).Should(gomega.ContainSubstring("guild_id=386659935687147521"))
+}