Add OAuth2 authorization code flow (auth.oauth2 module)

Co-authored-by: intel352 <77607+intel352@users.noreply.github.com>

Author: Copilot

cmd/server/data/featureflags.db-shm

@@ -10,6 +10,7 @@ require (
 )
 
 require (
+	cloud.google.com/go/compute/metadata v0.9.0 // indirect
 	github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c // indirect
 	github.com/BurntSushi/toml v1.6.0 // indirect
 	github.com/CrisisTextLine/modular/modules/auth v0.4.0 // indirect

cmd/server/data/featureflags.db-wal

@@ -1,3 +1,5 @@
+cloud.google.com/go/compute/metadata v0.9.0 h1:pDUj4QMoPejqq20dK0Pg2N4yG9zIkYGdBtwLoEkH9Zs=
+cloud.google.com/go/compute/metadata v0.9.0/go.mod h1:E0bWwX5wTnLPedCKqk3pJmVgCBSM6qQI1yTBdEb3C10=
 github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c h1:udKWzYgxTojEKWjV8V+WSxDXJ4NFATAsZjh8iIbsQIg=
 github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c/go.mod h1:xomTg63KZ2rFqZQzSB4Vz2SUXa1BpHTVz9L5PTmPC4E=
 github.com/BurntSushi/toml v1.6.0 h1:dRaEfpa2VI55EwlIW72hMRHdWouJeRF7TPYhI+AUQjk=

example/go.mod

@@ -52,6 +52,7 @@ require (
 )
 
 require (
+	cloud.google.com/go/compute/metadata v0.9.0 // indirect
 	github.com/BurntSushi/toml v1.6.0 // indirect
 	github.com/DataDog/datadog-go/v5 v5.4.0 // indirect
 	github.com/Microsoft/go-winio v0.5.0 // indirect

example/go.sum

@@ -1,3 +1,5 @@
+cloud.google.com/go/compute/metadata v0.9.0 h1:pDUj4QMoPejqq20dK0Pg2N4yG9zIkYGdBtwLoEkH9Zs=
+cloud.google.com/go/compute/metadata v0.9.0/go.mod h1:E0bWwX5wTnLPedCKqk3pJmVgCBSM6qQI1yTBdEb3C10=
 github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c h1:udKWzYgxTojEKWjV8V+WSxDXJ4NFATAsZjh8iIbsQIg=
 github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c/go.mod h1:xomTg63KZ2rFqZQzSB4Vz2SUXa1BpHTVz9L5PTmPC4E=
 github.com/BurntSushi/toml v1.6.0 h1:dRaEfpa2VI55EwlIW72hMRHdWouJeRF7TPYhI+AUQjk=