feat(rust): honor pre-computed Entra ID auth for Azure /messages (#34107)

* feat(rust): honor pre-computed Entra ID (Authorization: Bearer) auth for Azure /messages

* harden Rust Azure auth gate to require a non-empty Bearer token, not header presence

litellm-rust/crates/ai-gateway/src/messages/common_utils.rs

@@ -50,3 +50,15 @@ pub(super) fn has_header(headers: &[(String, String)], name: &str) -> bool {
         .iter()
         .any(|(key, _)| key.eq_ignore_ascii_case(name))
 }
+
+pub(super) fn has_bearer_auth(headers: &[(String, String)]) -> bool {
+    headers.iter().any(|(name, value)| {
+        if !name.eq_ignore_ascii_case("authorization") {
+            return false;
+        }
+        let value = value.trim();
+        value.len() > 7
+            && value[..7].eq_ignore_ascii_case("bearer ")
+            && !value[7..].trim().is_empty()
+    })
+}

litellm-rust/crates/ai-gateway/src/messages/prepare.rs

@@ -3,7 +3,7 @@ use litellm_core::CoreResult;
 use litellm_core::messages::transformation::MessagesAuthStrategy;
 use litellm_core::routing_utils::provider::{CustomLlmProvider, get_custom_llm_provider};
 
-use super::common_utils::{has_header, messages_provider_config, string_headers};
+use super::common_utils::{has_bearer_auth, has_header, messages_provider_config, string_headers};
 use super::types::{MessagesRequest, ProviderMessagesRequest};
 
 pub(super) fn prepare_messages_call(
@@ -33,7 +33,9 @@ pub(super) fn prepare_messages_call(
     let mut headers = string_headers(request.extra_headers)?;
 
     let auth_strategy = config.auth_strategy();
-    if !has_header(&headers, auth_strategy.header_name()) {
+    let already_authorized = has_header(&headers, auth_strategy.header_name())
+        || (config.accepts_bearer_auth() && has_bearer_auth(&headers));
+    if !already_authorized {
         let api_key = config.resolve_api_key(request.api_key, &env_lookup)?;
         let auth_header = match auth_strategy {
             MessagesAuthStrategy::Bearer => {

litellm-rust/crates/ai-gateway/src/messages/tests.rs

@@ -6,7 +6,7 @@ use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::net::{TcpListener, TcpStream};
 
 use super::common_utils::{
-    has_header, messages_provider_config, string_headers, truncate_error_body,
+    has_bearer_auth, has_header, messages_provider_config, string_headers, truncate_error_body,
 };
 use super::{MessagesRequest, messages};
 
@@ -85,6 +85,34 @@ fn has_header_is_case_insensitive() {
     assert!(!has_header(&headers, "authorization"));
 }
 
+#[test]
+fn has_bearer_auth_requires_a_nonempty_bearer_token() {
+    assert!(has_bearer_auth(&[(
+        "Authorization".to_string(),
+        "Bearer tok".to_string()
+    )]));
+    assert!(has_bearer_auth(&[(
+        "authorization".to_string(),
+        "bearer tok".to_string()
+    )]));
+    assert!(!has_bearer_auth(&[(
+        "authorization".to_string(),
+        "Bearer ".to_string()
+    )]));
+    assert!(!has_bearer_auth(&[(
+        "authorization".to_string(),
+        String::new()
+    )]));
+    assert!(!has_bearer_auth(&[(
+        "authorization".to_string(),
+        "Basic abc".to_string()
+    )]));
+    assert!(!has_bearer_auth(&[(
+        "x-api-key".to_string(),
+        "sk".to_string()
+    )]));
+}
+
 #[tokio::test]
 async fn messages_round_trip_builds_azure_request_and_passes_response_through() {
     let listener = TcpListener::bind("127.0.0.1:0").await.expect("binds");
@@ -252,6 +280,112 @@ async fn messages_does_not_duplicate_auth_when_x_api_key_supplied() {
     assert!(!head.contains("rust-fallback-key"), "{head}");
 }
 
+#[tokio::test]
+async fn messages_forwards_entra_id_bearer_without_requiring_api_key() {
+    let listener = TcpListener::bind("127.0.0.1:0").await.expect("binds");
+    let addr = listener.local_addr().expect("addr");
+
+    let server = tokio::spawn(async move {
+        let (mut socket, _) = listener.accept().await.expect("accepts request");
+        let request = read_http_request(&mut socket).await;
+        let response_body =
+            r#"{"id":"msg_3","type":"message","role":"assistant","content":[],"model":"m"}"#;
+        socket
+            .write_all(write_response(response_body).as_bytes())
+            .await
+            .expect("writes response");
+        request
+    });
+
+    let mut headers = Map::new();
+    headers.insert(
+        "Authorization".to_string(),
+        Value::String("Bearer entra-token".to_string()),
+    );
+
+    messages(MessagesRequest {
+        model: "claude-sonnet-4-5",
+        body: json!({"model": "claude-sonnet-4-5", "max_tokens": 8, "messages": []}),
+        api_key: None,
+        api_base: Some(&format!("http://{addr}")),
+        custom_llm_provider: Some("azure_ai"),
+        extra_headers: Some(headers),
+        timeout: Some(Duration::from_secs(5)),
+    })
+    .await
+    .expect("entra id request succeeds without api key");
+
+    let request = server.await.expect("server task completes");
+    let head = request
+        .split_once("\r\n\r\n")
+        .expect("has body")
+        .0
+        .to_ascii_lowercase();
+    assert!(head.contains("authorization: bearer entra-token"), "{head}");
+    assert!(!head.contains("x-api-key"), "{head}");
+}
+
+#[tokio::test]
+async fn messages_requires_auth_when_no_key_and_no_header() {
+    let err = messages(MessagesRequest {
+        model: "claude-sonnet-4-5",
+        body: json!({"model": "claude-sonnet-4-5", "max_tokens": 8, "messages": []}),
+        api_key: None,
+        api_base: Some("http://127.0.0.1:1"),
+        custom_llm_provider: Some("azure_ai"),
+        extra_headers: None,
+        timeout: Some(Duration::from_millis(50)),
+    })
+    .await
+    .expect_err("missing auth errors");
+
+    assert!(matches!(err, CoreError::Auth(_)));
+}
+
+#[tokio::test]
+async fn messages_ignores_malformed_authorization_and_uses_api_key() {
+    let listener = TcpListener::bind("127.0.0.1:0").await.expect("binds");
+    let addr = listener.local_addr().expect("addr");
+
+    let server = tokio::spawn(async move {
+        let (mut socket, _) = listener.accept().await.expect("accepts request");
+        let request = read_http_request(&mut socket).await;
+        let response_body =
+            r#"{"id":"msg_4","type":"message","role":"assistant","content":[],"model":"m"}"#;
+        socket
+            .write_all(write_response(response_body).as_bytes())
+            .await
+            .expect("writes response");
+        request
+    });
+
+    let mut headers = Map::new();
+    headers.insert(
+        "Authorization".to_string(),
+        Value::String("Bearer ".to_string()),
+    );
+
+    messages(MessagesRequest {
+        model: "claude-sonnet-4-5",
+        body: json!({"model": "claude-sonnet-4-5", "max_tokens": 8, "messages": []}),
+        api_key: Some("sk-azure"),
+        api_base: Some(&format!("http://{addr}")),
+        custom_llm_provider: Some("azure_ai"),
+        extra_headers: Some(headers),
+        timeout: Some(Duration::from_secs(5)),
+    })
+    .await
+    .expect("falls back to api key");
+
+    let request = server.await.expect("server task completes");
+    let head = request
+        .split_once("\r\n\r\n")
+        .expect("has body")
+        .0
+        .to_ascii_lowercase();
+    assert!(head.contains("x-api-key: sk-azure"), "{head}");
+}
+
 #[tokio::test]
 async fn messages_maps_provider_error_status_to_http_error() {
     let listener = TcpListener::bind("127.0.0.1:0").await.expect("binds");

litellm-rust/crates/core/src/messages/transformation.rs

@@ -35,6 +35,10 @@ pub trait AnthropicMessagesProviderConfig: Sync {
         MessagesAuthStrategy::Header("x-api-key")
     }
 
+    fn accepts_bearer_auth(&self) -> bool {
+        false
+    }
+
     fn default_headers(&self) -> &'static [(&'static str, &'static str)] {
         &[
             ("anthropic-version", "2023-06-01"),

litellm-rust/crates/core/src/providers/azure_ai/messages/transformation.rs

@@ -163,6 +163,10 @@ impl AnthropicMessagesProviderConfig for AzureAnthropicMessagesConfig {
         self.anthropic.auth_strategy()
     }
 
+    fn accepts_bearer_auth(&self) -> bool {
+        true
+    }
+
     fn default_headers(&self) -> &'static [(&'static str, &'static str)] {
         self.anthropic.default_headers()
     }
@@ -294,6 +298,11 @@ mod tests {
         );
     }
 
+    #[test]
+    fn accepts_bearer_auth_for_entra_id() {
+        assert!(AZURE_ANTHROPIC_MESSAGES_CONFIG.accepts_bearer_auth());
+    }
+
     #[test]
     fn default_headers_match_python() {
         assert_eq!(