Add SEP-991 (CIMD) support for URL-based client IDs (#570)

* feat(auth): add cimd support for SEP-991

add cimd support for url-based client ids

Signed-off-by: tanish111 <tanishdesai37@gmail.com>

* test(auth): add unit tests for is_https_url helper

Add test coverage for is_https_url helper to validate HTTPS scheme, non-root paths,
and reject http, javascript, data schemes, and invalid inputs per SEP-991 requirements.

Signed-off-by: tanish111 <tanishdesai37@gmail.com>

* feat(example): add CIMD OAuth server for SEP-991 testing

Implements a new server example (servers_cimd_auth_streamhttp) that
demonstrates CIMD (Client ID Metadata Document) support for URL-based
client IDs. The server validates client_id URLs, fetches and validates
client metadata documents, and provides OAuth 2.0 authorization endpoints
with MCP integration for end-to-end testing.

Signed-off-by: tanish111 <tanishdesai37@gmail.com>

* fix(oauth): add CORS headers to token endpoint

Add CORS headers to token endpoint to allow cross-origin requests from browsers
during OAuth authorization code exchange flow.

Signed-off-by: tanish111 <tanishdesai37@gmail.com>

* refactor: improve is_https_url function and consolidate tests

- Improve is_https_url function formatting and readability
- Merge all test cases into single test_is_https_url_scenarios function
- Add missing test case for "https://" URL

Signed-off-by: tanish111 <tanishdesai37@gmail.com>

* refactor: use map_err instead of match for error handling in auth.rs

Replace the verbose match statement with
map_err for more idiomatic

Signed-off-by: tanish111 <tanishdesai37@gmail.com>

* feat: add client-metadata.json

Add client metadata file for SEP-991 CIMD
authentication support

Signed-off-by: tanish111 <tanishdesai37@gmail.com>

---------

Signed-off-by: tanish111 <tanishdesai37@gmail.com>

examples/servers/Cargo.toml

@@ -44,6 +44,7 @@ tower-http = { version = "0.6", features = ["cors"] }
 hyper = { version = "1" }
 hyper-util = { version = "0", features = ["server"] }
 tokio-util = { version = "0.7" }
+url = "2.5"
 
 [dev-dependencies]
 tokio-stream = { version = "0.1" }
@@ -97,6 +98,10 @@ path = "src/simple_auth_streamhttp.rs"
 name = "servers_complex_auth_streamhttp"
 path = "src/complex_auth_streamhttp.rs"
 
+[[example]]
+name = "servers_cimd_auth_streamhttp"
+path = "src/cimd_auth_streamhttp.rs"
+
 [[example]]
 name = "servers_calculator_stdio"
 path = "src/calculator_stdio.rs"