BEIJING — A secretive meeting between North Korea’s Kim Jong Un and China’s Xi Jinping this week showcased enduring bonds between the two countries, highlighting the diplomatic challenge facing President Donald Trump. Kim, making what was believed to be his first foreign trip as leader, arrived in Beijing aboard a slow armored train on Monday and met with Xi and other senior Chinese officials, according to North Korean and Chinese media. The “unofficial” visit, which was not announced until after Kim left China, came just weeks before the North Korean leader is scheduled to see South Korea President Moon Jae-in, followed by a planned summit with Trump. The Beijing meeting, analysts said, was staged to show that North Korea-China ties are back on track, as underscored by photographs of energetic handshakes and an account of a heartfelt toast from Kim. The message to the United States: Any moves on North Korea must go through Xi. Trump showcased China’s gatekeeper role in a tweet Wednesday, saying Xi told him that plans for a U.S.-North Korea summit appear on track. “Received message last night from XI JINPING of China that his meeting with KIM JONG UN went very well and that KIM looks forward to his meeting with me,” Trump wrote.