diff --git a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/DefaultSaml2AuthenticatedPrincipal.java b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/DefaultSaml2AuthenticatedPrincipal.java
index db478be3ab..131f88bf58 100644
--- a/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/DefaultSaml2AuthenticatedPrincipal.java
+++ b/saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/DefaultSaml2AuthenticatedPrincipal.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.io.Serializable;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 
 import org.springframework.util.Assert;
 
@@ -78,4 +79,20 @@ public class DefaultSaml2AuthenticatedPrincipal implements Saml2AuthenticatedPri
 		this.registrationId = registrationId;
 	}
 
+	@Override
+	public boolean equals(Object object) {
+		if (this == object) {
+			return true;
+		}
+		if (!(object instanceof DefaultSaml2AuthenticatedPrincipal that)) {
+			return false;
+		}
+		return Objects.equals(this.name, that.name) && Objects.equals(this.registrationId, that.registrationId);
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(this.name, this.registrationId);
+	}
+
 }
diff --git a/saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/DefaultSaml2AuthenticatedPrincipalTests.java b/saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/DefaultSaml2AuthenticatedPrincipalTests.java
index 1b9b33fb7c..4ea06059a6 100644
--- a/saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/DefaultSaml2AuthenticatedPrincipalTests.java
+++ b/saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/DefaultSaml2AuthenticatedPrincipalTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -81,4 +81,24 @@ public class DefaultSaml2AuthenticatedPrincipalTests {
 		assertThat((Instant) registrationInfo.get(1)).isEqualTo(registeredDate);
 	}
 
+	// gh-15346
+	@Test
+	public void whenUsedAsKeyInMapThenRetrievableAcrossSerialization() {
+		Map<Saml2AuthenticatedPrincipal, Integer> valuesByPrincipal = new LinkedHashMap<>();
+		DefaultSaml2AuthenticatedPrincipal principal = new DefaultSaml2AuthenticatedPrincipal("user", Map.of());
+		valuesByPrincipal.put(principal, 1);
+		principal = new DefaultSaml2AuthenticatedPrincipal("user", Map.of());
+		assertThat(valuesByPrincipal.get(principal)).isEqualTo(1);
+		principal = new DefaultSaml2AuthenticatedPrincipal("user", Map.of());
+		principal.setRelyingPartyRegistrationId("id");
+		assertThat(valuesByPrincipal.get(principal)).isNull();
+		valuesByPrincipal.put(principal, 2);
+		principal = new DefaultSaml2AuthenticatedPrincipal("user", Map.of());
+		principal.setRelyingPartyRegistrationId("id");
+		assertThat(valuesByPrincipal.get(principal)).isEqualTo(2);
+		principal = new DefaultSaml2AuthenticatedPrincipal("USER", Map.of());
+		principal.setRelyingPartyRegistrationId("id");
+		assertThat(valuesByPrincipal.get(principal)).isNull();
+	}
+
 }