private modifyAquireTokenFunction(): void {
        const originalAquireToken = AdalService.prototype.acquireToken;
        const that = this;

        AdalService.prototype.acquireToken = function (resource): Observable<any> {
            var _this = this;   // save outer this for inner function

            let errorMessage: string;
            return Observable.bindCallback(acquireTokenInternal, function (token: string) {
                if (!token && errorMessage)
                    throw (errorMessage);
                return token;
            })();

            function acquireTokenInternal(cb: any) {
                let s: string = null;

                _this.adalContext.acquireToken(resource, (error: string, tokenOut: string) => {
                    if (error) {
                        _this.adalContext.error('Error when acquiring token for resource: ' + resource, error);
                        errorMessage = error;
                        that.ngZone.run(() => {
                            cb(<string>null);
                        })
                    } else {
                        that.ngZone.run(() => {
                            cb(tokenOut);
                            s = tokenOut;
                        })
                    }
                });
                return s;
            }
        };
    }