Add a setting to allow anonymous access to individual gists while still RequireLogin everywhere else (#229)

* Add a setting to allow accessing individual gists without auth

This is a middle ground between the existing setting "Require Login",
which requires login to do anything at all, and having it off, which
shows a public list of gists and more generally allows discovering info
about the users/gists of the instance without login.

The idea of this setting is that it is "require login" for everything
except individual gists.

Fixes #228.


Co-authored-by: Thomas Miceli <tho.miceli@gmail.com>

internal/web/auth.go

@@ -442,3 +442,15 @@ func getAvatarUrlFromProvider(provider string, identifier string) string {
 	}
 	return ""
 }
+
+type ContextAuthInfo struct {
+	context echo.Context
+}
+
+func (auth ContextAuthInfo) RequireLogin() (bool, error) {
+	return getData(auth.context, "RequireLogin") == true, nil
+}
+
+func (auth ContextAuthInfo) AllowGistsWithoutLogin() (bool, error) {
+	return getData(auth.context, "AllowGistsWithoutLogin") == true, nil
+}