Fediverse-based authentication (#1846)

* Able to authenticate user against IndieAuth. For #1273

* WIP server indieauth endpoint. For https://github.com/owncast/owncast/issues/1272

* Add migration to remove access tokens from user

* Add authenticated bool to user for display purposes

* Add indieauth modal and auth flair to display names. For #1273

* Validate URLs and display errors

* Renames, cleanups

* Handle relative auth endpoint paths. Add error handling for missing redirects.

* Disallow using display names in use by registered users. Closes #1810

* Verify code verifier via code challenge on callback

* Use relative path to authorization_endpoint

* Post-rebase fixes

* Use a timestamp instead of a bool for authenticated

* Propertly handle and display error in modal

* Use auth'ed timestamp to derive authenticated flag to display in chat

* Fediverse chat auth via OTP

* Increase validity time just in case

* Add fediverse auth into auth modal

* Text, validation, cleanup updates for fedi auth

* Fix typo

* Remove unused images

* Remove unused file

* Add chat display name to auth modal text

auth/fediverse/fediverse_test.go

@@ -0,0 +1,43 @@
+package fediverse
+
+import "testing"
+
+const (
+	accessToken     = "fake-access-token"
+	account         = "blah"
+	userID          = "fake-user-id"
+	userDisplayName = "fake-user-display-name"
+)
+
+func TestOTPFlowValidation(t *testing.T) {
+	r := RegisterFediverseOTP(accessToken, userID, userDisplayName, account)
+
+	if r.Code == "" {
+		t.Error("Code is empty")
+	}
+
+	if r.Account != account {
+		t.Error("Account is not set correctly")
+	}
+
+	if r.Timestamp.IsZero() {
+		t.Error("Timestamp is empty")
+	}
+
+	valid, registration := ValidateFediverseOTP(accessToken, r.Code)
+	if !valid {
+		t.Error("Code is not valid")
+	}
+
+	if registration.Account != account {
+		t.Error("Account is not set correctly")
+	}
+
+	if registration.UserID != userID {
+		t.Error("UserID is not set correctly")
+	}
+
+	if registration.UserDisplayName != userDisplayName {
+		t.Error("UserDisplayName is not set correctly")
+	}
+}