Add `DnsRebindingProtection` Ktor route-scoped plugin and enable it by
default across all http transports
## Motivation and Context
DNS rebinding protection was disabled by default
(`enableDnsRebindingProtection = false`), and sse endpoints
(`Route.mcp()`) had zero protection. Same vulnerability as typescript
sdk
[GHSA-w48q-cv73-mx4w](https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-w48q-cv73-mx4w)
## How Has This Been Tested?
all tests pass
## Breaking Changes
- `Route.mcp()`, `Application.mcp()` signatures changed (new
`enableDnsRebindingProtection`, `allowedHosts`, `allowedOrigins`
params), binary incompatible on JVM
- `enableDnsRebindingProtection` default changed from `false` to `true`
on `mcpStreamableHttp`/`mcpStatelessStreamableHttp`
- Default allowed hosts: `localhost`, `127.0.0.1`, `[::1]` — opt out
with `enableDnsRebindingProtection = false`
- Host validation is now port-agnostic (matches ts sdk)
- Origin validation now allows missing `Origin` header (non-browser
clients)
- `Configuration.enableDnsRebindingProtection`, `.allowedHosts`,
`.allowedOrigins` deprecated in favor of the plugin
## Types of changes
- [x] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
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