Logs provider name on startup

If invalid provider is specified, stop and error out

fixes #895

CHANGELOG.md

@@ -17,6 +17,7 @@
 
 ## Breaking Changes
 
+- [#911](https://github.com/oauth2-proxy/oauth2-rpoxy/pull/911) Specifying a non-existent provider will cause OAuth2-Proxy to fail on startup instead of defaulting to "google".
 - [#722](https://github.com/oauth2-proxy/oauth2-proxy/pull/722) When a Redis session store is configured, OAuth2-Proxy will fail to start up unless connection and health checks to Redis pass
 - [#800](https://github.com/oauth2-proxy/oauth2-proxy/pull/800) Fix import path for v7. The import path has changed to support the go get installation.
   - You can now `go get github.com/oauth2-proxy/oauth2-proxy/v7` to get the latest `v7` version of OAuth2 Proxy
@@ -34,6 +35,7 @@
 
 ## Changes since v6.1.1
 
+- [#911](https://github.com/oauth2-proxy/oauth2-rpoxy/pull/911) Validate provider type on startup.
 - [#906](https://github.com/oauth2-proxy/oauth2-proxy/pull/906) Set up v6.1.x versioned documentation as default documentation (@JoelSpeed)
 - [#905](https://github.com/oauth2-proxy/oauth2-proxy/pull/905) Remove v5 legacy sessions support (@NickMeves)
 - [#904](https://github.com/oauth2-proxy/oauth2-proxy/pull/904) Set `skip-auth-strip-headers` to `true` by default (@NickMeves)

pkg/validation/options.go

@@ -233,7 +233,13 @@ func parseProviderInfo(o *options.Options, msgs []string) []string {
 	p.ValidateURL, msgs = parseURL(o.ValidateURL, "validate", msgs)
 	p.ProtectedResource, msgs = parseURL(o.ProtectedResource, "resource", msgs)
 
-	o.SetProvider(providers.New(o.ProviderType, p))
+	provider := providers.New(o.ProviderType, p)
+	if provider == nil {
+		msgs = append(msgs, fmt.Sprintf("invalid setting: provider '%s' is not available", o.ProviderType))
+		return msgs
+	}
+	o.SetProvider(provider)
+
 	switch p := o.GetProvider().(type) {
 	case *providers.AzureProvider:
 		p.Configure(o.AzureTenant)

providers/providers.go

@@ -46,7 +46,9 @@ func New(provider string, p *ProviderData) Provider {
 		return NewNextcloudProvider(p)
 	case "digitalocean":
 		return NewDigitalOceanProvider(p)
-	default:
+	case "google":
 		return NewGoogleProvider(p)
+	default:
+		return nil
 	}
 }