feat: add support for authenticated datafile access

[jaeopt]

Summary

• add support for authenticated datafile access
• auth-token can be set by calling either
  (1) Optimizely optimizely = OptimizelyFactory.newDefaultInstance(String sdkKey,
  String authDatafileToken,
  String fallback); or
  (2) HttpProjectConfigManager.Builder builder = HttpProjectConfigManager.builder()
  .withSdkKey(sdkKey)
  .withAuthDatafileToken(authDatafileToken);
  Optimizely optimizely = OptimizelyFactory.newDefaultInstance(builder.build());

Test plan

• test the target url and authenticated header are set appropriately both when auth-token is specified (authenticated datafile) or not (regular datafaile)

[coveralls]

Pull Request Test Coverage Report for Build 1412

• 19 of 20 (95.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 89.472%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core-httpclient-impl/src/main/java/com/optimizely/ab/config/HttpProjectConfigManager.java	15	16	93.75%

Totals
Change from base Build 1401:	0.04%
Covered Lines:	3952
Relevant Lines:	4417

---

💛 - Coveralls

[mjc1283]

In other SDKs we named it datafileAuthToken, could you please follow that for all variable & method names?

[mjc1283]

Should createHttpRequest be private?

[jaeopt]

Private must be right one. This default access will be useful for header testing.

[mjc1283]

Then let's use the VisibleForTesting annotation.

[mjc1283]

Then let's use the VisibleForTesting annotation.

[mikecdavis]

The cascading signatures here don't line up nicely. We should consistently call the next method in the chain.

public static Optimizely newDefaultInstance(String sdkKey) {
    ...
    return newDefaultInstance(sdkKey, null)
}

public static Optimizely newDefaultInstance(String sdkKey, String fallback) {
    ...
    String datafileAuthToken = PropertyUtils.get(HttpProjectConfigManager.CONFIG_SDK_AUTH_TOKEN);
    return newDefaultInstance(sdkKey, fallback, datafileAuthToken)
}

public static Optimizely newDefaultInstance(String sdkKey, String fallback, String datafileAuthToken) {
    ...
    return newDefaultInstance(builder.build(), notificationCenter);
}

Unfortunately these are all strings so order needs to be paid attention to. We should also provide a configuration option for datafileAuthToken so customers can deploy this via optimizely.properties and not have explicitly provide this value to the factory method. See the example above.

[mikeproeng37]

We've been using datafileAccessToken in the other SDKs. Let's stick with the same name throughout.

On vacation. Will get it reviewed later.

[pawels-optimizely]

lgtm