diff --git a/test/s3/iam/docker-compose.yml b/test/s3/iam/docker-compose.yml
index af9ad3be0..002505696 100644
--- a/test/s3/iam/docker-compose.yml
+++ b/test/s3/iam/docker-compose.yml
@@ -132,7 +132,7 @@ services:
 
   # Keycloak Setup Service
   keycloak-setup:
-    image: alpine/curl:latest
+    image: alpine/curl:8.4.0
     container_name: keycloak-setup
     volumes:
       - ./setup_keycloak_docker.sh:/setup.sh:ro
diff --git a/test/s3/iam/s3_iam_distributed_test.go b/test/s3/iam/s3_iam_distributed_test.go
index 0e45dd09e..f51900ee0 100644
--- a/test/s3/iam/s3_iam_distributed_test.go
+++ b/test/s3/iam/s3_iam_distributed_test.go
@@ -104,8 +104,8 @@ func TestS3IAMDistributedTests(t *testing.T) {
 
 	t.Run("distributed_concurrent_operations", func(t *testing.T) {
 		// Test concurrent operations across distributed instances
-		// CI-REALISTIC APPROACH: 8 total operations (4x2) - 33% more than original (6) with pragmatic CI tolerance
-		// Success rates vary from 62.5%-87.5% due to CI environment resource constraints, but system functions correctly
+		// STRINGENT APPROACH: 8 total operations (4x2) - 33% more than original (6) with rigorous error detection
+		// Target >87.5% success rate to catch concurrency regressions while allowing minimal CI infrastructure issues
 		const numGoroutines = 4             // Optimal concurrency for CI reliability
 		const numOperationsPerGoroutine = 2 // Minimal operations per goroutine
 
@@ -216,34 +216,33 @@ func TestS3IAMDistributedTests(t *testing.T) {
 			}
 		}
 
-		// CI-REALISTIC CONCURRENCY TESTING: Pragmatic thresholds based on observed CI environment variability
-		// For totalOperations=8, success rates vary 62.5%-87.5% due to CI infrastructure constraints
+		// STRINGENT CONCURRENCY TESTING: More rigorous thresholds to catch regressions while accounting for CI variability
+		// For totalOperations=8, target >87.5% success rate (≤12.5% error rate) to detect concurrency issues
 
-		// Serious errors (race conditions, deadlocks) should be minimal for reliable CI testing
-		// Allow up to 50% serious errors for CI environment variability (infrastructure limitations, volume allocation issues)
-		// This accounts for the reality that CI environments have resource constraints that can affect multiple operations
-		maxSeriousErrors := totalOperations / 2 // Realistic tolerance for CI infrastructure variability
+		// Serious errors (race conditions, deadlocks) should be very limited - allow only 1 for CI infrastructure issues
+		// Based on observed data: 1-3 errors due to volume allocation constraints, not actual concurrency bugs
+		maxSeriousErrors := 1 // Allow 1 serious error (12.5%) for CI infrastructure limitations only
 		if len(seriousErrors) > maxSeriousErrors {
 			t.Errorf("❌ %d serious error(s) detected (%.1f%%), exceeding threshold of %d. This indicates potential concurrency bugs. First error: %v",
 				len(seriousErrors), float64(len(seriousErrors))/float64(totalOperations)*100, maxSeriousErrors, seriousErrors[0])
 		}
 
-		// For total errors, use pragmatic thresholds based on observed CI environment variability
-		// CI environments can have resource constraints that affect multiple operations simultaneously
-		maxTotalErrorsStrict := 2  // Allow max 2 total errors (25% rate) - good performance in CI
-		maxTotalErrorsRelaxed := 4 // Allow max 4 total errors (50% rate) - acceptable for resource-constrained CI
+		// For total errors, use stringent thresholds to catch regressions while allowing minimal CI infrastructure issues
+		// Target >87.5% success rate to ensure system reliability and catch concurrency problems early
+		maxTotalErrorsStrict := 1  // Allow max 1 total error (12.5% rate) - excellent performance target
+		maxTotalErrorsRelaxed := 2 // Allow max 2 total errors (25% rate) - acceptable with infrastructure constraints
 
 		if len(errorList) > maxTotalErrorsRelaxed {
-			t.Errorf("❌ Too many total errors: %d (%.1f%%) - exceeds relaxed threshold of %d (%.1f%%). System is unstable under concurrent load.",
+			t.Errorf("❌ Too many total errors: %d (%.1f%%) - exceeds threshold of %d (%.1f%%). System may have concurrency issues.",
 				len(errorList), errorRate*100, maxTotalErrorsRelaxed, float64(maxTotalErrorsRelaxed)/float64(totalOperations)*100)
 		} else if len(errorList) > maxTotalErrorsStrict {
-			t.Logf("⚠️  Concurrent operations completed with %d errors (%.1f%%) - within relaxed CI limits. Normal CI environment variability.",
+			t.Logf("⚠️  Concurrent operations completed with %d errors (%.1f%%) - acceptable but monitor for patterns.",
 				len(errorList), errorRate*100)
 		} else if len(errorList) > 0 {
-			t.Logf("✅ Concurrent operations completed with %d errors (%.1f%%) - good performance for CI environment!",
+			t.Logf("✅ Concurrent operations completed with %d errors (%.1f%%) - excellent performance!",
 				len(errorList), errorRate*100)
 		} else {
-			t.Logf("🎉 All %d concurrent operations completed successfully - excellent CI performance!", totalOperations)
+			t.Logf("🎉 All %d concurrent operations completed successfully - perfect concurrency handling!", totalOperations)
 		}
 	})
 }
diff --git a/weed/iam/oidc/oidc_provider.go b/weed/iam/oidc/oidc_provider.go
index 6f0161cce..4a356d109 100644
--- a/weed/iam/oidc/oidc_provider.go
+++ b/weed/iam/oidc/oidc_provider.go
@@ -2,6 +2,8 @@ package oidc
 
 import (
 	"context"
+	"crypto/ecdsa"
+	"crypto/elliptic"
 	"crypto/rsa"
 	"encoding/base64"
 	"encoding/json"
@@ -490,6 +492,8 @@ func (p *OIDCProvider) parseJWK(key *JWK) (interface{}, error) {
 	switch key.Kty {
 	case "RSA":
 		return p.parseRSAKey(key)
+	case "EC":
+		return p.parseECKey(key)
 	default:
 		return nil, fmt.Errorf("unsupported key type: %s", key.Kty)
 	}
@@ -524,6 +528,53 @@ func (p *OIDCProvider) parseRSAKey(key *JWK) (*rsa.PublicKey, error) {
 	return pubKey, nil
 }
 
+// parseECKey parses an Elliptic Curve key from JWK
+func (p *OIDCProvider) parseECKey(key *JWK) (*ecdsa.PublicKey, error) {
+	// Validate required fields
+	if key.X == "" || key.Y == "" || key.Crv == "" {
+		return nil, fmt.Errorf("incomplete EC key: missing x, y, or crv parameter")
+	}
+
+	// Get the curve
+	var curve elliptic.Curve
+	switch key.Crv {
+	case "P-256":
+		curve = elliptic.P256()
+	case "P-384":
+		curve = elliptic.P384()
+	case "P-521":
+		curve = elliptic.P521()
+	default:
+		return nil, fmt.Errorf("unsupported EC curve: %s", key.Crv)
+	}
+
+	// Decode x coordinate
+	xBytes, err := base64.RawURLEncoding.DecodeString(key.X)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode EC x coordinate: %v", err)
+	}
+
+	// Decode y coordinate
+	yBytes, err := base64.RawURLEncoding.DecodeString(key.Y)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode EC y coordinate: %v", err)
+	}
+
+	// Create EC public key
+	pubKey := &ecdsa.PublicKey{
+		Curve: curve,
+		X:     new(big.Int).SetBytes(xBytes),
+		Y:     new(big.Int).SetBytes(yBytes),
+	}
+
+	// Validate that the point is on the curve
+	if !curve.IsOnCurve(pubKey.X, pubKey.Y) {
+		return nil, fmt.Errorf("EC key coordinates are not on the specified curve")
+	}
+
+	return pubKey, nil
+}
+
 // mapUserInfoToIdentity maps UserInfo response to ExternalIdentity
 func (p *OIDCProvider) mapUserInfoToIdentity(userInfo map[string]interface{}) *providers.ExternalIdentity {
 	identity := &providers.ExternalIdentity{
diff --git a/weed/iam/policy/aws_iam_compliance_test.go b/weed/iam/policy/aws_iam_compliance_test.go
index ad76367c1..0979589a5 100644
--- a/weed/iam/policy/aws_iam_compliance_test.go
+++ b/weed/iam/policy/aws_iam_compliance_test.go
@@ -200,7 +200,7 @@ func TestAWSWildcardMatch(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			result := awsWildcardMatch(tt.pattern, tt.value)
+			result := AwsWildcardMatch(tt.pattern, tt.value)
 			assert.Equal(t, tt.expected, result, "AWS wildcard match should match expected")
 		})
 	}
diff --git a/weed/iam/policy/policy_engine.go b/weed/iam/policy/policy_engine.go
index d063c5f2c..5f1ca0cb3 100644
--- a/weed/iam/policy/policy_engine.go
+++ b/weed/iam/policy/policy_engine.go
@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
+	"sync"
 )
 
 // Effect represents the policy evaluation result
@@ -17,6 +18,12 @@ const (
 	EffectDeny  Effect = "Deny"
 )
 
+// Package-level regex cache for performance optimization
+var (
+	regexCache   = make(map[string]*regexp.Regexp)
+	regexCacheMu sync.RWMutex
+)
+
 // PolicyEngine evaluates policies against requests
 type PolicyEngine struct {
 	config      *PolicyEngineConfig
@@ -624,7 +631,7 @@ func awsIAMMatch(pattern, value string, evalCtx *EvaluationContext) bool {
 
 	// Step 4: Handle AWS-style wildcards (case-insensitive)
 	if strings.Contains(expandedPattern, "*") || strings.Contains(expandedPattern, "?") {
-		return awsWildcardMatch(expandedPattern, value)
+		return AwsWildcardMatch(expandedPattern, value)
 	}
 
 	return false
@@ -666,19 +673,37 @@ func getContextValue(evalCtx *EvaluationContext, key, defaultValue string) strin
 	return defaultValue
 }
 
-// awsWildcardMatch performs case-insensitive wildcard matching like AWS IAM
-func awsWildcardMatch(pattern, value string) bool {
-	// Convert pattern to regex with case-insensitive matching
-	// AWS uses * for any sequence and ? for any single character
+// AwsWildcardMatch performs case-insensitive wildcard matching like AWS IAM
+func AwsWildcardMatch(pattern, value string) bool {
+	// Create regex pattern key for caching
 	regexPattern := strings.ReplaceAll(pattern, "*", ".*")
 	regexPattern = strings.ReplaceAll(regexPattern, "?", ".")
 	regexPattern = "^" + regexPattern + "$"
+	regexKey := "(?i)" + regexPattern
 
-	// Compile with case-insensitive flag
-	regex, err := regexp.Compile("(?i)" + regexPattern)
-	if err != nil {
-		// Fallback to simple case-insensitive comparison if regex fails
-		return strings.EqualFold(pattern, value)
+	// Try to get compiled regex from cache
+	regexCacheMu.RLock()
+	regex, found := regexCache[regexKey]
+	regexCacheMu.RUnlock()
+
+	if !found {
+		// Compile and cache the regex
+		compiledRegex, err := regexp.Compile(regexKey)
+		if err != nil {
+			// Fallback to simple case-insensitive comparison if regex fails
+			return strings.EqualFold(pattern, value)
+		}
+
+		// Store in cache with write lock
+		regexCacheMu.Lock()
+		// Double-check in case another goroutine added it
+		if existingRegex, exists := regexCache[regexKey]; exists {
+			regex = existingRegex
+		} else {
+			regexCache[regexKey] = compiledRegex
+			regex = compiledRegex
+		}
+		regexCacheMu.Unlock()
 	}
 
 	return regex.MatchString(value)
diff --git a/weed/iam/providers/provider.go b/weed/iam/providers/provider.go
index 6f1e3ca14..5c1deb03d 100644
--- a/weed/iam/providers/provider.go
+++ b/weed/iam/providers/provider.go
@@ -4,11 +4,10 @@ import (
 	"context"
 	"fmt"
 	"net/mail"
-	"regexp"
-	"strings"
 	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
+	"github.com/seaweedfs/seaweedfs/weed/iam/policy"
 )
 
 // IdentityProvider defines the interface for external identity providers
@@ -222,26 +221,7 @@ func (r *MappingRule) Matches(claims *TokenClaims) bool {
 // matchValue checks if a value matches the rule value (with wildcard support)
 // Uses AWS IAM-compliant case-insensitive wildcard matching for consistency with policy engine
 func (r *MappingRule) matchValue(value string) bool {
-	matched := awsWildcardMatch(r.Value, value)
+	matched := policy.AwsWildcardMatch(r.Value, value)
 	glog.V(3).Infof("AWS IAM pattern match result: '%s' matches '%s' = %t", value, r.Value, matched)
 	return matched
 }
-
-// awsWildcardMatch performs case-insensitive wildcard matching like AWS IAM
-// This function ensures consistent matching behavior across the IAM system
-func awsWildcardMatch(pattern, value string) bool {
-	// Convert pattern to regex with case-insensitive matching
-	// AWS uses * for any sequence and ? for any single character
-	regexPattern := strings.ReplaceAll(pattern, "*", ".*")
-	regexPattern = strings.ReplaceAll(regexPattern, "?", ".")
-	regexPattern = "^" + regexPattern + "$"
-
-	// Compile with case-insensitive flag
-	regex, err := regexp.Compile("(?i)" + regexPattern)
-	if err != nil {
-		// Fallback to simple case-insensitive comparison if regex fails
-		return strings.EqualFold(pattern, value)
-	}
-
-	return regex.MatchString(value)
-}
diff --git a/weed/iam/sts/security_test.go b/weed/iam/sts/security_test.go
new file mode 100644
index 000000000..dec65a9db
--- /dev/null
+++ b/weed/iam/sts/security_test.go
@@ -0,0 +1,192 @@
+package sts
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+	"github.com/seaweedfs/seaweedfs/weed/iam/providers"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestSecurityIssuerToProviderMapping tests the security fix that ensures JWT tokens
+// with specific issuer claims can only be validated by the provider registered for that issuer
+func TestSecurityIssuerToProviderMapping(t *testing.T) {
+	ctx := context.Background()
+
+	// Create STS service with two mock providers
+	service := NewSTSService()
+	config := &STSConfig{
+		TokenDuration:    time.Hour,
+		MaxSessionLength: time.Hour * 12,
+		Issuer:           "test-sts",
+		SigningKey:       []byte("test-signing-key-32-characters-long"),
+	}
+
+	err := service.Initialize(config)
+	require.NoError(t, err)
+
+	// Set up mock trust policy validator
+	mockValidator := &MockTrustPolicyValidator{}
+	service.SetTrustPolicyValidator(mockValidator)
+
+	// Create two mock providers with different issuers
+	providerA := &MockIdentityProviderWithIssuer{
+		name:   "provider-a",
+		issuer: "https://provider-a.com",
+		validTokens: map[string]bool{
+			"token-for-provider-a": true,
+		},
+	}
+
+	providerB := &MockIdentityProviderWithIssuer{
+		name:   "provider-b",
+		issuer: "https://provider-b.com",
+		validTokens: map[string]bool{
+			"token-for-provider-b": true,
+		},
+	}
+
+	// Register both providers
+	err = service.RegisterProvider(providerA)
+	require.NoError(t, err)
+	err = service.RegisterProvider(providerB)
+	require.NoError(t, err)
+
+	// Create JWT tokens with specific issuer claims
+	tokenForProviderA := createTestJWT(t, "https://provider-a.com", "user-a")
+	tokenForProviderB := createTestJWT(t, "https://provider-b.com", "user-b")
+
+	t.Run("jwt_token_with_issuer_a_only_validated_by_provider_a", func(t *testing.T) {
+		// This should succeed - token has issuer A and provider A is registered
+		identity, provider, err := service.validateWebIdentityToken(ctx, tokenForProviderA)
+		assert.NoError(t, err)
+		assert.NotNil(t, identity)
+		assert.Equal(t, "provider-a", provider.Name())
+	})
+
+	t.Run("jwt_token_with_issuer_b_only_validated_by_provider_b", func(t *testing.T) {
+		// This should succeed - token has issuer B and provider B is registered
+		identity, provider, err := service.validateWebIdentityToken(ctx, tokenForProviderB)
+		assert.NoError(t, err)
+		assert.NotNil(t, identity)
+		assert.Equal(t, "provider-b", provider.Name())
+	})
+
+	t.Run("jwt_token_with_unregistered_issuer_fails", func(t *testing.T) {
+		// Create token with unregistered issuer
+		tokenWithUnknownIssuer := createTestJWT(t, "https://unknown-issuer.com", "user-x")
+
+		// This should fail - no provider registered for this issuer
+		identity, provider, err := service.validateWebIdentityToken(ctx, tokenWithUnknownIssuer)
+		assert.Error(t, err)
+		assert.Nil(t, identity)
+		assert.Nil(t, provider)
+		assert.Contains(t, err.Error(), "no identity provider registered for issuer: https://unknown-issuer.com")
+	})
+
+	t.Run("non_jwt_tokens_still_work_with_fallback", func(t *testing.T) {
+		// Non-JWT tokens should still work via fallback mechanism
+		identity, provider, err := service.validateWebIdentityToken(ctx, "token-for-provider-a")
+		assert.NoError(t, err)
+		assert.NotNil(t, identity)
+		assert.Equal(t, "provider-a", provider.Name())
+	})
+}
+
+// createTestJWT creates a test JWT token with the specified issuer and subject
+func createTestJWT(t *testing.T, issuer, subject string) string {
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
+		"iss": issuer,
+		"sub": subject,
+		"aud": "test-client",
+		"exp": time.Now().Add(time.Hour).Unix(),
+		"iat": time.Now().Unix(),
+	})
+
+	tokenString, err := token.SignedString([]byte("test-signing-key"))
+	require.NoError(t, err)
+	return tokenString
+}
+
+// MockIdentityProviderWithIssuer is a mock provider that supports issuer mapping
+type MockIdentityProviderWithIssuer struct {
+	name        string
+	issuer      string
+	validTokens map[string]bool
+}
+
+func (m *MockIdentityProviderWithIssuer) Name() string {
+	return m.name
+}
+
+func (m *MockIdentityProviderWithIssuer) GetIssuer() string {
+	return m.issuer
+}
+
+func (m *MockIdentityProviderWithIssuer) Initialize(config interface{}) error {
+	return nil
+}
+
+func (m *MockIdentityProviderWithIssuer) Authenticate(ctx context.Context, token string) (*providers.ExternalIdentity, error) {
+	// For JWT tokens, parse and validate the token format
+	if len(token) > 50 && strings.Contains(token, ".") {
+		// This looks like a JWT - parse it to get the subject
+		parsedToken, _, err := new(jwt.Parser).ParseUnverified(token, jwt.MapClaims{})
+		if err != nil {
+			return nil, fmt.Errorf("invalid JWT token")
+		}
+
+		claims, ok := parsedToken.Claims.(jwt.MapClaims)
+		if !ok {
+			return nil, fmt.Errorf("invalid claims")
+		}
+
+		issuer, _ := claims["iss"].(string)
+		subject, _ := claims["sub"].(string)
+
+		// Verify the issuer matches what we expect
+		if issuer != m.issuer {
+			return nil, fmt.Errorf("token issuer %s does not match provider issuer %s", issuer, m.issuer)
+		}
+
+		return &providers.ExternalIdentity{
+			UserID:   subject,
+			Email:    subject + "@" + m.name + ".com",
+			Provider: m.name,
+		}, nil
+	}
+
+	// For non-JWT tokens, check our simple token list
+	if m.validTokens[token] {
+		return &providers.ExternalIdentity{
+			UserID:   "test-user",
+			Email:    "test@" + m.name + ".com",
+			Provider: m.name,
+		}, nil
+	}
+
+	return nil, fmt.Errorf("invalid token")
+}
+
+func (m *MockIdentityProviderWithIssuer) GetUserInfo(ctx context.Context, userID string) (*providers.ExternalIdentity, error) {
+	return &providers.ExternalIdentity{
+		UserID:   userID,
+		Email:    userID + "@" + m.name + ".com",
+		Provider: m.name,
+	}, nil
+}
+
+func (m *MockIdentityProviderWithIssuer) ValidateToken(ctx context.Context, token string) (*providers.TokenClaims, error) {
+	if m.validTokens[token] {
+		return &providers.TokenClaims{
+			Subject: "test-user",
+			Issuer:  m.issuer,
+		}, nil
+	}
+	return nil, fmt.Errorf("invalid token")
+}
diff --git a/weed/iam/sts/sts_service.go b/weed/iam/sts/sts_service.go
index 4808f0be0..4ef216edc 100644
--- a/weed/iam/sts/sts_service.go
+++ b/weed/iam/sts/sts_service.go
@@ -346,6 +346,11 @@ func (s *STSService) AssumeRoleWithWebIdentity(ctx context.Context, request *Ass
 		return nil, fmt.Errorf("invalid request: %w", err)
 	}
 
+	// Check for unsupported session policy
+	if request.Policy != nil {
+		return nil, fmt.Errorf("session policies are not currently supported - Policy parameter must be omitted")
+	}
+
 	// 1. Validate the web identity token with appropriate provider
 	externalIdentity, provider, err := s.validateWebIdentityToken(ctx, request.WebIdentityToken)
 	if err != nil {
@@ -542,29 +547,44 @@ func (s *STSService) validateAssumeRoleWithWebIdentityRequest(request *AssumeRol
 	return nil
 }
 
-// validateWebIdentityToken validates the web identity token with available providers
+// validateWebIdentityToken validates the web identity token with strict issuer-to-provider mapping
+// SECURITY: JWT tokens with a specific issuer claim MUST only be validated by the provider for that issuer
 func (s *STSService) validateWebIdentityToken(ctx context.Context, token string) (*providers.ExternalIdentity, providers.IdentityProvider, error) {
-	// First, try efficient issuer-based lookup
+	// Try to extract issuer from JWT token for strict validation
 	issuer, err := s.extractIssuerFromJWT(token)
-	if err == nil {
-		// Look up provider by issuer for O(1) efficiency
-		if provider, exists := s.issuerToProvider[issuer]; exists {
-			identity, err := provider.Authenticate(ctx, token)
-			if err == nil && identity != nil {
-				return identity, provider, nil
-			}
-			// If authentication fails with the expected provider, don't continue
-			// This prevents tokens from being validated by wrong providers
-			return nil, nil, fmt.Errorf("token validation failed with issuer %s: %w", issuer, err)
-		}
-
-		glog.V(2).Infof("No provider registered for issuer %s, falling back to brute-force search", issuer)
-	} else {
-		glog.V(2).Infof("Could not extract issuer from token (%v), falling back to brute-force search", err)
+	if err != nil {
+		// Token is not a valid JWT or cannot be parsed
+		// This can happen with non-JWT providers (e.g., LDAP) or test tokens
+		// For backward compatibility with non-JWT tokens, fall back to trying all providers
+		glog.V(2).Infof("Token is not a valid JWT (%v), falling back to all providers", err)
+		return s.validateWithAllProviders(ctx, token)
 	}
 
-	// Fallback: try all providers (backward compatibility)
-	// This handles providers that don't have issuer mapping or malformed tokens
+	// Look up the specific provider for this issuer
+	provider, exists := s.issuerToProvider[issuer]
+	if !exists {
+		// SECURITY: If no provider is registered for this issuer, fail immediately
+		// This prevents JWT tokens from being validated by unintended providers
+		return nil, nil, fmt.Errorf("no identity provider registered for issuer: %s", issuer)
+	}
+
+	// Authenticate with the correct provider for this issuer
+	identity, err := provider.Authenticate(ctx, token)
+	if err != nil {
+		return nil, nil, fmt.Errorf("token validation failed with provider for issuer %s: %w", issuer, err)
+	}
+
+	if identity == nil {
+		return nil, nil, fmt.Errorf("authentication succeeded but no identity returned for issuer %s", issuer)
+	}
+
+	return identity, provider, nil
+}
+
+// validateWithAllProviders is a fallback for non-JWT tokens (e.g., LDAP credentials, test tokens)
+// This should only be used when the token is not a valid JWT
+func (s *STSService) validateWithAllProviders(ctx context.Context, token string) (*providers.ExternalIdentity, providers.IdentityProvider, error) {
+	// Try each provider until one succeeds
 	for _, provider := range s.providers {
 		identity, err := provider.Authenticate(ctx, token)
 		if err == nil && identity != nil {
@@ -572,7 +592,7 @@ func (s *STSService) validateWebIdentityToken(ctx context.Context, token string)
 		}
 	}
 
-	return nil, nil, fmt.Errorf("web identity token validation failed with all providers")
+	return nil, nil, fmt.Errorf("token validation failed with all providers")
 }
 
 // extractIssuerFromJWT extracts the issuer (iss) claim from a JWT token without verification
diff --git a/weed/iam/sts/sts_service_test.go b/weed/iam/sts/sts_service_test.go
index 7c1eee98e..2a5d568a1 100644
--- a/weed/iam/sts/sts_service_test.go
+++ b/weed/iam/sts/sts_service_test.go
@@ -410,3 +410,14 @@ func (m *MockIdentityProvider) ValidateToken(ctx context.Context, token string)
 	}
 	return nil, fmt.Errorf("invalid token")
 }
+
+// GetIssuer returns the issuer for this provider (for OIDC providers)
+func (m *MockIdentityProvider) GetIssuer() string {
+	// For OIDC mock provider, return the issuer from the first valid token
+	// This matches the issuer in the token claims
+	if m.name == "test-oidc" {
+		return "test-issuer"
+	}
+	// LDAP providers don't have issuers
+	return ""
+}
diff --git a/weed/s3api/s3_iam_middleware.go b/weed/s3api/s3_iam_middleware.go
index 4cb45c520..fd169e01c 100644
--- a/weed/s3api/s3_iam_middleware.go
+++ b/weed/s3api/s3_iam_middleware.go
@@ -6,6 +6,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"sort"
 	"strings"
 	"time"
 
@@ -769,14 +770,25 @@ func (s3iam *S3IAMIntegration) validateOIDCToken(ctx context.Context, token stri
 		}
 
 		// Parse roles (stored as comma-separated string)
-		roles := strings.Split(rolesAttr, ",")
-		if len(roles) == 0 {
+		rolesStr := strings.TrimSpace(rolesAttr)
+		roles := strings.Split(rolesStr, ",")
+
+		// Clean up role names
+		var cleanRoles []string
+		for _, role := range roles {
+			cleanRole := strings.TrimSpace(role)
+			if cleanRole != "" {
+				cleanRoles = append(cleanRoles, cleanRole)
+			}
+		}
+
+		if len(cleanRoles) == 0 {
 			glog.V(3).Infof("Empty roles list from provider %s", providerName)
 			continue
 		}
 
-		// Use the first role as the primary role
-		roleArn := roles[0]
+		// Determine the primary role using intelligent selection
+		roleArn := s3iam.selectPrimaryRole(cleanRoles, externalIdentity)
 
 		return &OIDCIdentity{
 			UserID:   externalIdentity.UserID,
@@ -788,6 +800,80 @@ func (s3iam *S3IAMIntegration) validateOIDCToken(ctx context.Context, token stri
 	return nil, fmt.Errorf("token not valid for any registered OIDC provider")
 }
 
+// selectPrimaryRole intelligently selects the primary role from multiple available roles
+// This provides deterministic role selection to prevent unpredictable access control behavior
+func (s3iam *S3IAMIntegration) selectPrimaryRole(roles []string, externalIdentity *providers.ExternalIdentity) string {
+	if len(roles) == 1 {
+		return roles[0]
+	}
+
+	glog.V(2).Infof("🔍 selectPrimaryRole: Selecting from %d roles: %v", len(roles), roles)
+
+	// Strategy 1: Check for explicit primary_role claim
+	if primaryRole, exists := externalIdentity.Attributes["primary_role"]; exists && primaryRole != "" {
+		primaryRole = strings.TrimSpace(primaryRole)
+		// Verify the primary role is in the available roles list
+		for _, role := range roles {
+			if strings.EqualFold(role, primaryRole) {
+				glog.V(2).Infof("🔍 selectPrimaryRole: Using explicit primary_role: %s", role)
+				return role
+			}
+		}
+		glog.V(1).Infof("⚠️ selectPrimaryRole: primary_role '%s' not found in available roles, falling back", primaryRole)
+	}
+
+	// Strategy 2: Role hierarchy - select most privileged role
+	selectedRole := s3iam.selectByRoleHierarchy(roles)
+	if selectedRole != "" {
+		glog.V(2).Infof("🔍 selectPrimaryRole: Using hierarchical selection: %s", selectedRole)
+		return selectedRole
+	}
+
+	// Strategy 3: Deterministic fallback - alphabetical order (consistent behavior)
+	sort.Strings(roles)
+	glog.V(2).Infof("🔍 selectPrimaryRole: Using deterministic selection (first alphabetically): %s", roles[0])
+	return roles[0]
+}
+
+// selectByRoleHierarchy selects a role based on predefined privilege hierarchy
+// Returns the most privileged role available, or empty string if no hierarchy match
+func (s3iam *S3IAMIntegration) selectByRoleHierarchy(roles []string) string {
+	// Define role hierarchy from most privileged to least privileged
+	// This covers common enterprise role naming patterns
+	roleHierarchy := [][]string{
+		// Tier 1: Super Admin roles
+		{"SuperAdmin", "super-admin", "super_admin", "root", "owner"},
+
+		// Tier 2: Admin roles
+		{"Admin", "admin", "Administrator", "administrator", "system-admin", "system_admin"},
+
+		// Tier 3: Manager/Power User roles
+		{"Manager", "manager", "PowerUser", "power-user", "power_user", "lead", "supervisor"},
+
+		// Tier 4: Editor/Write roles
+		{"Editor", "editor", "Writer", "writer", "Contributor", "contributor", "write", "readwrite", "read-write"},
+
+		// Tier 5: Viewer/Read roles
+		{"Viewer", "viewer", "Reader", "reader", "read-only", "read_only", "readonly", "read", "guest"},
+	}
+
+	// Find the highest priority role available
+	for _, tier := range roleHierarchy {
+		for _, privilegedRole := range tier {
+			for _, availableRole := range roles {
+				// Check for exact match or contains match (case-insensitive)
+				if strings.EqualFold(availableRole, privilegedRole) ||
+					strings.Contains(strings.ToLower(availableRole), strings.ToLower(privilegedRole)) {
+					return availableRole
+				}
+			}
+		}
+	}
+
+	// No hierarchy match found
+	return ""
+}
+
 // getProviderNames returns a list of provider names for debugging
 func getProviderNames(providers map[string]providers.IdentityProvider) []string {
 	names := make([]string, 0, len(providers))
diff --git a/weed/s3api/s3_iam_role_selection_test.go b/weed/s3api/s3_iam_role_selection_test.go
new file mode 100644
index 000000000..d6f1cba56
--- /dev/null
+++ b/weed/s3api/s3_iam_role_selection_test.go
@@ -0,0 +1,259 @@
+package s3api
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/iam/providers"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSelectPrimaryRole(t *testing.T) {
+	s3iam := &S3IAMIntegration{}
+
+	t.Run("single_role_returns_that_role", func(t *testing.T) {
+		roles := []string{"admin"}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: make(map[string]string),
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "admin", result)
+	})
+
+	t.Run("explicit_primary_role_takes_precedence", func(t *testing.T) {
+		roles := []string{"admin", "reader", "writer"}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: map[string]string{
+				"primary_role": "reader",
+			},
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "reader", result)
+	})
+
+	t.Run("explicit_primary_role_case_insensitive", func(t *testing.T) {
+		roles := []string{"Admin", "Reader", "Writer"}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: map[string]string{
+				"primary_role": "admin",
+			},
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "Admin", result)
+	})
+
+	t.Run("invalid_primary_role_falls_back_to_hierarchy", func(t *testing.T) {
+		roles := []string{"admin", "reader", "writer"}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: map[string]string{
+				"primary_role": "nonexistent",
+			},
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "admin", result) // Should select admin via hierarchy
+	})
+
+	t.Run("hierarchy_selection_admin_over_reader", func(t *testing.T) {
+		roles := []string{"reader", "admin", "writer"}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: make(map[string]string),
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "admin", result) // Admin has higher priority
+	})
+
+	t.Run("hierarchy_selection_case_insensitive", func(t *testing.T) {
+		roles := []string{"Reader", "ADMIN", "writer"}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: make(map[string]string),
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "ADMIN", result)
+	})
+
+	t.Run("hierarchy_selection_contains_match", func(t *testing.T) {
+		roles := []string{"system-reader", "system-admin-user", "system-writer"}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: make(map[string]string),
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "system-admin-user", result) // Contains "admin"
+	})
+
+	t.Run("deterministic_fallback_alphabetical", func(t *testing.T) {
+		// Roles that don't match any hierarchy
+		roles := []string{"zebra", "alpha", "beta"}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: make(map[string]string),
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "alpha", result) // First alphabetically
+	})
+
+	t.Run("complex_enterprise_roles", func(t *testing.T) {
+		roles := []string{
+			"app-user-readonly",
+			"app-user-contributor",
+			"app-admin-full",
+			"system-guest",
+		}
+		externalIdentity := &providers.ExternalIdentity{
+			Attributes: make(map[string]string),
+		}
+
+		result := s3iam.selectPrimaryRole(roles, externalIdentity)
+		assert.Equal(t, "app-admin-full", result) // Contains "admin"
+	})
+}
+
+func TestSelectByRoleHierarchy(t *testing.T) {
+	s3iam := &S3IAMIntegration{}
+
+	t.Run("super_admin_highest_priority", func(t *testing.T) {
+		roles := []string{"admin", "super-admin", "reader"}
+		result := s3iam.selectByRoleHierarchy(roles)
+		assert.Equal(t, "super-admin", result)
+	})
+
+	t.Run("admin_over_manager", func(t *testing.T) {
+		roles := []string{"manager", "admin", "reader"}
+		result := s3iam.selectByRoleHierarchy(roles)
+		assert.Equal(t, "admin", result)
+	})
+
+	t.Run("manager_over_editor", func(t *testing.T) {
+		roles := []string{"editor", "manager", "reader"}
+		result := s3iam.selectByRoleHierarchy(roles)
+		assert.Equal(t, "manager", result)
+	})
+
+	t.Run("editor_over_viewer", func(t *testing.T) {
+		roles := []string{"viewer", "editor"}
+		result := s3iam.selectByRoleHierarchy(roles)
+		assert.Equal(t, "editor", result)
+	})
+
+	t.Run("no_hierarchy_match_returns_empty", func(t *testing.T) {
+		roles := []string{"custom-role-1", "custom-role-2", "special-user"}
+		result := s3iam.selectByRoleHierarchy(roles)
+		assert.Equal(t, "", result)
+	})
+
+	t.Run("multiple_same_tier_returns_first_found", func(t *testing.T) {
+		roles := []string{"viewer", "reader", "guest"}
+		result := s3iam.selectByRoleHierarchy(roles)
+		// Should return first match found in the hierarchy (viewer comes first in tier definition)
+		assert.Equal(t, "viewer", result)
+	})
+
+	t.Run("case_variations", func(t *testing.T) {
+		roles := []string{"ADMIN", "Reader", "writer"}
+		result := s3iam.selectByRoleHierarchy(roles)
+		assert.Equal(t, "ADMIN", result)
+	})
+}
+
+func TestRoleSelectionIntegration(t *testing.T) {
+	t.Run("real_world_enterprise_scenario", func(t *testing.T) {
+		// Simulate a real enterprise OIDC token with multiple roles
+		testCases := []struct {
+			name          string
+			roles         []string
+			primaryRole   string // explicit primary_role claim
+			expectedRole  string
+			selectionType string
+		}{
+			{
+				name:          "explicit_primary_overrides_hierarchy",
+				roles:         []string{"admin", "reader", "writer"},
+				primaryRole:   "reader",
+				expectedRole:  "reader",
+				selectionType: "explicit",
+			},
+			{
+				name:          "hierarchy_selects_admin_over_others",
+				roles:         []string{"contributor", "admin", "viewer"},
+				primaryRole:   "", // No explicit primary
+				expectedRole:  "admin",
+				selectionType: "hierarchy",
+			},
+			{
+				name:          "deterministic_fallback_for_unknown_roles",
+				roles:         []string{"zebra-role", "alpha-role", "beta-role"},
+				primaryRole:   "",
+				expectedRole:  "alpha-role",
+				selectionType: "deterministic",
+			},
+			{
+				name:          "complex_enterprise_naming",
+				roles:         []string{"org-user-readonly", "org-power-user", "org-system-admin"},
+				primaryRole:   "",
+				expectedRole:  "org-system-admin", // Contains "admin"
+				selectionType: "hierarchy",
+			},
+		}
+
+		s3iam := &S3IAMIntegration{}
+
+		for _, tc := range testCases {
+			t.Run(tc.name, func(t *testing.T) {
+				externalIdentity := &providers.ExternalIdentity{
+					Attributes: make(map[string]string),
+				}
+				if tc.primaryRole != "" {
+					externalIdentity.Attributes["primary_role"] = tc.primaryRole
+				}
+
+				result := s3iam.selectPrimaryRole(tc.roles, externalIdentity)
+				assert.Equal(t, tc.expectedRole, result,
+					"Expected %s selection to return %s, got %s",
+					tc.selectionType, tc.expectedRole, result)
+			})
+		}
+	})
+}
+
+// Test helper function to verify role parsing improvements
+func TestRoleParsingImprovements(t *testing.T) {
+	t.Run("whitespace_handling", func(t *testing.T) {
+		// Test the improved role parsing logic
+		rolesStr := " admin , reader , writer "
+		roles := strings.Split(rolesStr, ",")
+
+		// Clean up role names (this is what the main code does now)
+		var cleanRoles []string
+		for _, role := range roles {
+			cleanRole := strings.TrimSpace(role)
+			if cleanRole != "" {
+				cleanRoles = append(cleanRoles, cleanRole)
+			}
+		}
+
+		expected := []string{"admin", "reader", "writer"}
+		assert.Equal(t, expected, cleanRoles)
+	})
+
+	t.Run("empty_roles_filtered", func(t *testing.T) {
+		rolesStr := "admin,,reader, ,writer"
+		roles := strings.Split(rolesStr, ",")
+
+		var cleanRoles []string
+		for _, role := range roles {
+			cleanRole := strings.TrimSpace(role)
+			if cleanRole != "" {
+				cleanRoles = append(cleanRoles, cleanRole)
+			}
+		}
+
+		expected := []string{"admin", "reader", "writer"}
+		assert.Equal(t, expected, cleanRoles)
+	})
+}