Introduce setDefaultAuth(auth) top level method

Author: Joe Goggins

src/Particle.js

@@ -2099,6 +2099,15 @@ class Particle {
 		});
 	}
 
+	/**
+	 * Set default auth token that will be used in each method if `auth` is not provided
+	 * @param  {String} auth A Particle access token
+	 * @returns {undefined}
+	 */
+	setDefaultAuth(auth){
+		this._defaultAuth = auth;
+	}
+
 	/**
 	 * API URI to access a device
 	 * @param  {Object} options Options for this API call

test/Particle.spec.js

@@ -2716,4 +2716,16 @@ describe('ParticleAPI', () => {
 			expect(api.agent.setBaseUrl.firstCall.args[0]).to.eql(baseUrl);
 		});
 	});
+
+	describe('setDefaultAuth(auth)', () => {
+		afterEach(() => {
+			sinon.restore();
+		});
+
+		it('sets ._defaultAuth', () => {
+			const auth = 'foo';
+			api.setDefaultAuth(auth);
+			expect(api._defaultAuth).to.eql(auth);
+		});
+	});
 });