diff --git a/crates/iam/src/oidc.rs b/crates/iam/src/oidc.rs
index b3d68016a..f28f3b9ff 100644
--- a/crates/iam/src/oidc.rs
+++ b/crates/iam/src/oidc.rs
@@ -833,18 +833,38 @@ impl OidcSys {
     async fn discover_provider(config: &OidcProviderConfig, http_client: &ReqwestHttpClient) -> Result<ProviderState, String> {
         // The openidconnect crate expects the issuer URL (base), not the
         // .well-known/openid-configuration URL.
-        let issuer_str = normalize_config_url(&config.config_url)?;
+        let base_issuer = normalize_config_url(&config.config_url)?;
+        let candidates = issuer_candidates(&base_issuer);
+        let mut last_errors = Vec::new();
 
-        let issuer_url = IssuerUrl::new(issuer_str).map_err(|e| format!("invalid issuer URL: {e}"))?;
+        for candidate_issuer in candidates.iter() {
+            let issuer_url = IssuerUrl::new(candidate_issuer.clone()).map_err(|e| format!("invalid issuer URL: {e}"))?;
 
-        let metadata = CoreProviderMetadata::discover_async(issuer_url, http_client)
-            .await
-            .map_err(|e| format!("discovery failed: {e}"))?;
+            match CoreProviderMetadata::discover_async(issuer_url, http_client)
+                .await
+                .map_err(|e| format!("discovery failed: {e}"))
+            {
+                Ok(metadata) => {
+                    return Ok(ProviderState {
+                        metadata,
+                        discovered_at: Instant::now(),
+                    });
+                }
+                Err(error) => {
+                    last_errors.push(format!("issuer '{candidate_issuer}': {error}"));
+                    warn!(
+                        "OIDC provider '{}' discovery attempt failed for issuer '{}': {}",
+                        config.id, candidate_issuer, error
+                    );
+                }
+            }
+        }
 
-        Ok(ProviderState {
-            metadata,
-            discovered_at: Instant::now(),
-        })
+        Err(format!(
+            "discovery failed for all issuer variants {:?}: {}",
+            candidates,
+            last_errors.join("; ")
+        ))
     }
 }
 
@@ -959,6 +979,21 @@ fn normalize_config_url(config_url: &str) -> Result<String, String> {
     Ok(issuer)
 }
 
+fn issuer_candidates(base: &str) -> Vec<String> {
+    let original = base.trim();
+    let mut variants = Vec::with_capacity(2);
+    variants.push(original.to_string());
+
+    let toggled = if original.ends_with('/') {
+        original.trim_end_matches('/').to_string()
+    } else {
+        format!("{original}/")
+    };
+    variants.push(toggled);
+
+    variants
+}
+
 /// Decode the payload section of a JWT without validation (token must already be verified).
 pub(crate) fn decode_jwt_payload(token: &str) -> HashMap<String, serde_json::Value> {
     let parts: Vec<&str> = token.split('.').collect();
@@ -1116,6 +1151,189 @@ mod tests {
         assert!(normalize_config_url("not-a-url").is_err());
     }
 
+    #[test]
+    fn test_issuer_candidates() {
+        assert_eq!(
+            issuer_candidates("https://idp.example.com/realm"),
+            vec![
+                "https://idp.example.com/realm".to_string(),
+                "https://idp.example.com/realm/".to_string()
+            ]
+        );
+        assert_eq!(
+            issuer_candidates("https://idp.example.com/realm/"),
+            vec![
+                "https://idp.example.com/realm/".to_string(),
+                "https://idp.example.com/realm".to_string()
+            ]
+        );
+        assert_eq!(
+            issuer_candidates("https://idp.example.com"),
+            vec!["https://idp.example.com".to_string(), "https://idp.example.com/".to_string()]
+        );
+    }
+
+    fn build_mocked_oidc_provider_config(id: &str, config_url: &str) -> OidcProviderConfig {
+        OidcProviderConfig {
+            id: id.to_string(),
+            enabled: true,
+            config_url: config_url.to_string(),
+            client_id: "rustfs-oidc-test".to_string(),
+            client_secret: None,
+            scopes: vec!["openid".to_string()],
+            redirect_uri: None,
+            redirect_uri_dynamic: false,
+            claim_name: "sub".to_string(),
+            claim_prefix: "oidc".to_string(),
+            role_policy: String::new(),
+            display_name: "mock-oidc".to_string(),
+            groups_claim: "groups".to_string(),
+            email_claim: "email".to_string(),
+            username_claim: "username".to_string(),
+        }
+    }
+
+    fn start_mock_oidc_discovery_server<F>(
+        build_discovery_issuer: F,
+        max_requests: usize,
+    ) -> (String, std::thread::JoinHandle<()>)
+    where
+        F: Fn(&str) -> String + Send + 'static,
+    {
+        use std::io::Read;
+        use std::io::Write;
+        use std::net::{Shutdown, TcpListener};
+        use std::time::{Duration, Instant};
+
+        // After the last completed response, exit if no new connection arrives within this window.
+        const IDLE_SHUTDOWN: Duration = Duration::from_millis(100);
+        const ABSOLUTE_CAP: Duration = Duration::from_millis(500);
+
+        let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+        let base = format!("http://{}", listener.local_addr().unwrap());
+        let discovery_issuer = build_discovery_issuer(&base);
+        let discovery_body = serde_json::json!({
+            "issuer": discovery_issuer,
+            "authorization_endpoint": format!("{base}/authorize"),
+            "token_endpoint": format!("{base}/token"),
+            "jwks_uri": format!("{base}/jwks"),
+            "response_types_supported": ["code"],
+            "response_modes_supported": ["query"],
+            "subject_types_supported": ["public"],
+            "id_token_signing_alg_values_supported": ["RS256"],
+        })
+        .to_string();
+        let jwks_body = r#"{"keys":[]}"#;
+
+        let handle = std::thread::spawn(move || {
+            listener
+                .set_nonblocking(true)
+                .expect("failed to set discovery mock listener non-blocking");
+
+            let mut seen = 0usize;
+            let start = Instant::now();
+            let mut last_completed = Instant::now();
+
+            loop {
+                if seen > 0 && last_completed.elapsed() >= IDLE_SHUTDOWN {
+                    break;
+                }
+                if start.elapsed() >= ABSOLUTE_CAP {
+                    break;
+                }
+
+                let mut stream = match listener.accept() {
+                    Ok((stream, _)) => stream,
+                    Err(e) if e.kind() == std::io::ErrorKind::WouldBlock => {
+                        std::thread::sleep(Duration::from_millis(5));
+                        continue;
+                    }
+                    Err(_) => break,
+                };
+
+                seen += 1;
+
+                let mut request_bytes = Vec::new();
+                let mut buffer = [0u8; 4096];
+                loop {
+                    let n = stream.read(&mut buffer).unwrap_or_default();
+                    if n == 0 {
+                        break;
+                    }
+                    request_bytes.extend_from_slice(&buffer[..n]);
+                    if request_bytes.windows(4).any(|w| w == b"\r\n\r\n") {
+                        break;
+                    }
+                    if request_bytes.len() >= 8192 {
+                        break;
+                    }
+                }
+                let request = String::from_utf8_lossy(&request_bytes);
+                let path = request.lines().next().unwrap_or("").split_whitespace().nth(1).unwrap_or("");
+
+                let (status, body) = if path.contains("/.well-known/openid-configuration") {
+                    (200, discovery_body.as_str())
+                } else if path.contains("/jwks") {
+                    (200, jwks_body)
+                } else {
+                    (404, r#"{"error":"not found"}"#)
+                };
+
+                let response = format!(
+                    "HTTP/1.1 {status} {}\r\nContent-Type: application/json\r\nContent-Length: {}\r\nConnection: close\r\n\r\n{body}",
+                    if status == 200 { "OK" } else { "Not Found" },
+                    body.len()
+                );
+
+                let _ = stream.write_all(response.as_bytes());
+                let _ = stream.flush();
+                let _ = stream.shutdown(Shutdown::Both);
+                last_completed = Instant::now();
+
+                if seen >= max_requests {
+                    break;
+                }
+            }
+        });
+
+        (base, handle)
+    }
+
+    fn discovery_error_contains_all_variants(err: &str, base: &str) -> bool {
+        err.contains(base) && err.contains(&format!("{base}/")) && err.contains("discovery failed for all issuer variants")
+    }
+
+    #[tokio::test]
+    async fn test_validate_oidc_provider_config_retries_with_issuer_candidates() {
+        // Discovery document must advertise the canonical issuer path. The first candidate has no
+        // trailing slash; openidconnect rejects issuer mismatch, then the second variant succeeds.
+        let (base, handle) = start_mock_oidc_discovery_server(|base| format!("{base}/application/o/rustfs/"), 8);
+        let config_url = format!("{base}/application/o/rustfs");
+        let config = build_mocked_oidc_provider_config("default", &config_url);
+
+        let result = validate_oidc_provider_config(&config).await;
+
+        let validation_result = result.expect("OIDC provider validation should succeed");
+        assert_eq!(validation_result.issuer, format!("{base}/application/o/rustfs/"));
+        assert!(handle.join().is_ok());
+    }
+
+    #[tokio::test]
+    async fn test_validate_oidc_provider_config_returns_detailed_errors() {
+        let (base, handle) = start_mock_oidc_discovery_server(|base| format!("{base}/application/o/other"), 8);
+        let config_url = format!("{base}/application/o/rustfs");
+        let config = build_mocked_oidc_provider_config("default", &config_url);
+
+        let err = validate_oidc_provider_config(&config)
+            .await
+            .expect_err("OIDC provider validation should fail");
+        assert!(discovery_error_contains_all_variants(&err, &base));
+        assert!(err.contains("issuer '"));
+        assert!(err.contains(&format!("issuer '{base}/application/o/rustfs'")));
+        assert!(err.contains(&format!("issuer '{base}/application/o/rustfs/'")));
+        assert!(handle.join().is_ok());
+    }
+
     #[test]
     fn test_decode_jwt_payload_invalid() {
         assert!(decode_jwt_payload("not-a-jwt").is_empty());