419 support iam auth in replications

[smithsz]

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What

Support IAM authentication in replications. For example:

• Via replicator database:

  client.replicator()
      .source("https://foo.cloudant.com/src")
      .sourceIamApiKey("mysourcedbiamapikey")
      .target("https://bar.cloudant.com/tgt")
      .targetIamApiKey("mytargetdbiamapikey")
      .save();

• Via /_replicate endpoint:

  client.replication()
      .source("https://foo.cloudant.com/src")
      .sourceIamApiKey("mysourcedbiamapikey")
      .target("https://bar.cloudant.com/tgt")
      .targetIamApiKey("mytargetdbiamapikey")
      .trigger();

How

Expose new methods on the underlying replication document classes. These add the required IAM API key fields to the generated replication document JSON.

Example IAM authenticated replication document:

{
  "source": { "url": "...", "auth": { "iam": { "api_key": "<key>" } } },
  "target": { "url": "...", "auth": { "iam": { "api_key": "<key>" } } },
}

Testing

Includes additional mock unit tests.

Issues

Fixes #419.

[ricellis]

I think I'm +1 once that last utf8 piece is done