oidc: test stub IdP + happy-path exchange test

go.mod

@@ -4,24 +4,25 @@ go 1.25.0
 
 require (
 	github.com/coder/websocket v1.8.14
+	github.com/coreos/go-oidc/v3 v3.18.0
 	github.com/go-chi/chi/v5 v5.2.5
+	github.com/golang-jwt/jwt/v5 v5.3.1
 	github.com/oklog/ulid/v2 v2.1.1
 	github.com/robfig/cron/v3 v3.0.1
 	golang.org/x/crypto v0.50.0
+	golang.org/x/oauth2 v0.36.0
 	golang.org/x/sys v0.43.0
 	gopkg.in/yaml.v3 v3.0.1
 	modernc.org/sqlite v1.50.0
 )
 
 require (
-	github.com/coreos/go-oidc/v3 v3.18.0 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/go-jose/go-jose/v4 v4.1.4 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
-	golang.org/x/oauth2 v0.36.0 // indirect
 	modernc.org/libc v1.72.0 // indirect
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.11.0 // indirect