Use consistent header name for authorization header (#1948)

* Use consistent header name for authorization header

* Remove dependency on @azure/ms-rest-js

lib/typescript/botbuilder-skills/src/http/skillHttpAdapter.ts

@@ -12,8 +12,6 @@ import { SkillHttpBotAdapter } from './skillHttpBotAdapter';
  * 2. Call SkillHttpBotAdapter to process the incoming activity.
  */
 export class SkillHttpAdapter extends BotFrameworkAdapter {
-    private readonly authHeaderName: string = 'Authorization';
-
     private readonly botAdapter: IActivityHandler;
     private readonly authenticationProvider?: IAuthenticationProvider;
     private readonly telemetryClient?: BotTelemetryClient;
@@ -35,8 +33,7 @@ export class SkillHttpAdapter extends BotFrameworkAdapter {
         if (this.authenticationProvider) {
             // grab the auth header from the inbound http request
             // eslint-disable-next-line @typescript-eslint/tslint/config
-            const headers: { [header: string]: string | string[] | undefined } = req.headers;
-            const authHeader: string = <string> headers[this.authHeaderName];
+            const authHeader: string = req.headers.authorization || req.headers.Authorization || '';
             const authenticated: boolean = await this.authenticationProvider.authenticate(authHeader);
 
             if (!authenticated) {