* feat: adds an internal token exchange utility based on https://tools.ietf.org/html/rfc8693

* fix: add copyright and address other comments

* fix: fix formatting

* fix: fixes copyright again

* fix: revert pom changes

* fix: revert auto-value changes

* fix: remove gson and address other comments

* fix: fixes to StsRequestHandlerTest

* feat: adds base external account credentials class and support for file/url based external credentials

* fix: javadoc changes

* fix: address review comments

* fix: nits

* fix: fix broken test

* fix: format

* feat: implements AWS signature version 4 for signing requests

* fix: fix javadoc

* fix: address review comments

* fix: changes to visibility and addresses other review comments

* fix: removes sortedHeaderNames from AwsRequestSignature, uses MessageDigest, and misc changes

* feat: generate authorization header in AwsRequestSigner

* fix: address more review comments

* fix: use RuntimeExceptions instead of invalid state/argument

* fix: javadoc

* fix: handle invalid input in Builder & misc fixes

* fix: get dates at construction and no longer catch ParseException in AwsDates

* fix: refactor AwsDates

* feat: adds text/json credential source support to IdentityPoolCredentials

* fix: format

* fix: format

* fix: add missing changes to MockExternalAccountCredentialsTransport

* fix: change parseToken to take an InputStream

* fix: charsets

* fix: broken build

* fix: type null check

* feat: adds support for AWS credentials

* fix: address nits

* fix: remove Truth lib use in AwsCredentialsTest

* fix: address more review comments

* fix: assertEquals param order

* feat: retrieve region from environment variable for AWS Lambda

…for 3pi (#501)

* chore: use ImpersonatedCredentials for service account impersonation in ExternalAccountCredentials

* chore: add test for invalid service account impersonation url

* fix: update AwsCredentials credential source logic

* fix: remove TODOs

* fix: cleanup

* fix: code review nits

* fix: fix broken test

* fix: lint

…brary-java into byoid

…brary-java into byoid