v18.6.6

## Description

* Fixed tsh/Linux sending a too-large username for device trust. [#63387](https://github.com/gravitational/teleport/pull/63387)
* Fixed an issue where MCP JSON-RPC messages with mixed-case field names could be parsed inconsistently and re-serialized to lower cases. Teleport now enforces canonical lowercase JSON-RPC fields. [#63364](https://github.com/gravitational/teleport/pull/63364)
* Improved robustness of the Slack hosted plugin to reduce the likeliness of failed token refresh when experiencing external disruption. [#63344](https://github.com/gravitational/teleport/pull/63344)
* Fixed a bug affecting access list review queries for lists where the name is a prefix of another list name. [#63337](https://github.com/gravitational/teleport/pull/63337)
* Updated the OCI SDK to support new regions. [#63265](https://github.com/gravitational/teleport/pull/63265)
* Ensure application session rejections for untrusted devices are consistently audited as AppSessionStart failures after MFA. [#63149](https://github.com/gravitational/teleport/pull/63149)
* Added Helm chart support to the `teleport-event-handler configure` command. [#63147](https://github.com/gravitational/teleport/pull/63147)
* Added `tctl` support for removing `okta_assignment` internal resource should it be needed. [#62698](https://github.com/gravitational/teleport/pull/62698)

Enterprise:
* Prevented manual membership changes to SCIM-type access lists while enabling support for their reviews.
* Fixed the issue where Okta integration may not remove previously synced apps after plugin restart.

## Download

Download the current and previous releases of Teleport at https://goteleport.com/download.

## Plugins

Download the current release of Teleport plugins from the links below.
* Slack [Linux amd64](https://cdn.teleport.dev/teleport-access-slack-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/teleport-access-slack-v18.6.6-linux-arm64-bin.tar.gz) 
* Mattermost [Linux amd64](https://cdn.teleport.dev/teleport-access-mattermost-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/teleport-access-mattermost-v18.6.6-linux-arm64-bin.tar.gz)
* Discord [Linux amd64](https://cdn.teleport.dev/teleport-access-discord-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/teleport-access-discord-v18.6.6-linux-arm64-bin.tar.gz)
* Terraform Provider [Linux amd64](https://cdn.teleport.dev/terraform-provider-teleport-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/terraform-provider-teleport-v18.6.6-linux-arm64-bin.tar.gz) | [macOS amd64](https://cdn.teleport.dev/terraform-provider-teleport-v18.6.6-darwin-amd64-bin.tar.gz) | [macOS arm64](https://cdn.teleport.dev/terraform-provider-teleport-v18.6.6-darwin-arm64-bin.tar.gz) | [macOS universal](https://cdn.teleport.dev/terraform-provider-teleport-v18.6.6-darwin-universal-bin.tar.gz)
* Event Handler [Linux amd64](https://cdn.teleport.dev/teleport-event-handler-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/teleport-event-handler-v18.6.6-linux-arm64-bin.tar.gz) | [macOS amd64](https://cdn.teleport.dev/teleport-event-handler-v18.6.6-darwin-amd64-bin.tar.gz)
* PagerDuty [Linux amd64](https://cdn.teleport.dev/teleport-access-pagerduty-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/teleport-access-pagerduty-v18.6.6-linux-arm64-bin.tar.gz)
* Jira [Linux amd64](https://cdn.teleport.dev/teleport-access-jira-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/teleport-access-jira-v18.6.6-linux-arm64-bin.tar.gz)
* Email [Linux amd64](https://cdn.teleport.dev/teleport-access-email-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/teleport-access-email-v18.6.6-linux-arm64-bin.tar.gz)
* Microsoft Teams [Linux amd64](https://cdn.teleport.dev/teleport-access-msteams-v18.6.6-linux-amd64-bin.tar.gz) | [Linux arm64](https://cdn.teleport.dev/teleport-access-msteams-v18.6.6-linux-arm64-bin.tar.gz)