v1.28.0 Release

Bigtable

• feat(bigtable): Add asynchronous method for sampling row keys (#6561). Users
  that extend bigtable::DataClient and wish to use the new method will need to
  override PrepareAsyncSampleRowKeys().
• fix(bigtable): bigtable::Table::AsyncBulkApply() now respects the Retry and
  Backoff policies (#6510)

IAM

NOTE This release includes an experimental IAM client library. This
library is NOT GA and is likely to have breaking changes in the coming
months. Feel free to take a look, file issues, ask questions, and even
experiment with it, but do not ship production code using it yet.

• feature(iam): generate iam admin code (#6430)

Pub/Sub

• fix(pubsub): save refresh timer for cancellation (#6662)
• feat(pubsub): add ability to set the ack deadline extension (#6620)

Spanner

• feat(spanner): use multiple channels instead of multiple client for the
  multiple rows cpu benchmark (#6659)
• fix(spanner): do not warn about SessionPoolClockOption (#6619)

Storage

• feat(storage): recommend g::c::Options (#6640)
• feat(storage): support multiple channels in GCS+gRPC (#6593)
• feat(storage): round-robin stub for GCS+gRPC (#6584)
• fix(storage): compile GCS+gRPC with Windows+x86 (#6556)
• feat(storage): install rules for GCS+gRPC plugin (#6527)
• fix(storage): compile with GCC 11 in C++17 mode (#6501)
• feat: Support unified credentials (google::cloud::Credentials) to initialize
  both the REST and gRPC plugins with the same classes. (#6518)(#6531)(#6617)(#6488)(#6441)

Common Libraries

• feat: Add support for "unified" credentials, which allow applications to
  Configure the REST and gRPC-based libraries using the same credential classes
  Support complex credential types, such as service account impersonation
  With this release, only the storage library supports unified credentials.
  (#6617)(#6614)(#6531)(#6518)
• feat: an example using identity tokens with gRPC (#6583)
• feat: example using identity tokens (#6569)