Add username alias for Postgres's PGSimpleDataSource

Closes gh-25363

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jdbc/DataSourceBuilder.java

@@ -198,6 +198,8 @@ public final class DataSourceBuilder<T extends DataSource> {
 					create(classLoader, "oracle.jdbc.datasource.OracleDataSource", OracleDataSourceSettings::new));
 			addIfAvailable(this.allDataSourceSettings, create(classLoader, "org.h2.jdbcx.JdbcDataSource",
 					(type) -> new DataSourceSettings(type, (aliases) -> aliases.addAliases("username", "user"))));
+			addIfAvailable(this.allDataSourceSettings, create(classLoader, "org.postgresql.ds.PGSimpleDataSource",
+					(type) -> new DataSourceSettings(type, (aliases) -> aliases.addAliases("username", "user"))));
 		}
 
 		private static List<DataSourceSettings> resolveAvailableDataSourceSettings(ClassLoader classLoader) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jdbc/DataSourceBuilderTests.java

@@ -33,6 +33,7 @@ import org.h2.Driver;
 import org.h2.jdbcx.JdbcDataSource;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
+import org.postgresql.ds.PGSimpleDataSource;
 
 import org.springframework.jdbc.datasource.SimpleDriverDataSource;
 
@@ -129,6 +130,15 @@ class DataSourceBuilderTests {
 		assertThat(h2DataSource.getUser()).isEqualTo("test");
 	}
 
+	@Test
+	void dataSourceCanBeCreatedWithPGDataSource() {
+		this.dataSource = DataSourceBuilder.create().url("jdbc:postgresql://localhost/test")
+				.type(PGSimpleDataSource.class).username("test").build();
+		assertThat(this.dataSource).isInstanceOf(PGSimpleDataSource.class);
+		PGSimpleDataSource pgDataSource = (PGSimpleDataSource) this.dataSource;
+		assertThat(pgDataSource.getUser()).isEqualTo("test");
+	}
+
 	@Test
 	void dataSourceAliasesAreOnlyAppliedToRelevantDataSource() {
 		this.dataSource = DataSourceBuilder.create().url("jdbc:h2:test").type(TestDataSource.class).username("test")