Add ability to get provider by name from auth service

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@extollo/lib",
-  "version": "0.9.32",
+  "version": "0.9.33",
   "description": "The framework library that lifts up your code.",
   "main": "lib/index.js",
   "types": "lib/index.d.ts",

src/auth/Authentication.ts

@@ -27,6 +27,15 @@ export class Authentication extends Unit {
 
     protected providers: {[name: string]: LoginProvider<LoginProviderConfig>} = {}
 
+    getProvider(name: string): LoginProvider<LoginProviderConfig> {
+        const provider = this.providers[name]
+        if ( !provider ) {
+            throw new ErrorWithContext('Invalid auth provider name: ' + name, { name })
+        }
+
+        return provider
+    }
+
     async up(): Promise<void> {
         this.middleware.registerNamespace('@auth', this.getMiddlewareResolver())