OAuth2AccessTokenResponse.Builder.expiresIn works after withResponse

Closes gh-8702

Author: benba

oauth2/oauth2-core/src/main/java/org/springframework/security/oauth2/core/endpoint/OAuth2AccessTokenResponse.java

@@ -140,6 +140,7 @@ public Builder tokenType(OAuth2AccessToken.TokenType tokenType) {
 		 */
 		public Builder expiresIn(long expiresIn) {
 			this.expiresIn = expiresIn;
+			this.expiresAt = null;
 			return this;
 		}
 

oauth2/oauth2-core/src/test/java/org/springframework/security/oauth2/core/endpoint/OAuth2AccessTokenResponseTests.java

@@ -153,4 +153,22 @@ public void buildWhenResponseAndRefreshNullThenRefreshNull() {
 
 		assertThat(withResponse.getRefreshToken()).isNull();
 	}
+
+	@Test
+	public void buildWhenResponseThenChangeExpiresInThenExpiresAtMatchIssueAtPlusExpiresIn() {
+		long originalExpiresIn = 10;
+		OAuth2AccessTokenResponse tokenResponse = OAuth2AccessTokenResponse
+				.withToken(TOKEN_VALUE)
+				.tokenType(OAuth2AccessToken.TokenType.BEARER)
+				.expiresIn(originalExpiresIn)
+				.build();
+
+		long alteredExpiresIn = 30;
+		OAuth2AccessTokenResponse withResponse = OAuth2AccessTokenResponse.withResponse(tokenResponse)
+				.expiresIn(alteredExpiresIn)
+				.build();
+
+		assertThat(withResponse.getAccessToken().getExpiresAt()).isEqualTo(
+				withResponse.getAccessToken().getIssuedAt().plusSeconds(alteredExpiresIn));
+	}
 }