What is the authenticity and meaning of the Hadith "Of whomsoever I am Mawla, Ali is also his Mawla"?

There is disagreement regarding the authenticity of the hadith, "Of whomsoever I am the mawla, Ali is also his mawla." However, the authentic part of it—if proven—does not serve as evidence for the additional phrases that were appended to it to elevate Ali, may Allah be pleased with him, above the rest of the Companions, or to disparage them. There has been disagreement about the meaning of the hadith, yet it does not contradict that Abu Bakr, Umar, Uthman, and Ali, may Allah be pleased with them, are the most deserving of the Caliphate in that order, and that Abu Bakr is the best of the Ummah. Among the interpretations of its meaning are: "Whomever I love, Ali loves him," or "Whoever takes me as a patron, Ali takes him as a patron," or the walaya (allegiance/patronage) of Islam, meaning that Allah is the patron of those who believe. It is not correct to interpret the walaya in it as referring to imamate (leadership) and the authority to manage the affairs of Muslims, because the independent authority during the lifetime of the Prophet, peace be upon him, was the Prophet himself. Therefore, it must be interpreted as referring to love, the walaya of Islam, and similar meanings.