On 14 January 2016, Alfaro was selected in the second round (27th overall) of the 2016 MLS SuperDraft by Seattle Sounders FC.[3] He signed a professional contract with the club two months later.[4]
On 25 March 2016, Alfaro made his professional debut for USL affiliate club Seattle Sounders FC 2 in a match against Sacramento Republic and conceded a penalty in the 62nd minute. Sacramento would convert their PK and win 1–0.[5]
On 4 March 2018, Alfaro received a red card in the 83rd minute, as the Sounders lost its opening game of the 2018 season 1–0 to recent expansion team Los Angeles FC.[6]
Guadalajara
In December 2018, Alfaro passed a trial with C.D. Guadalajara and was signed as a free agent.[7] He spent time on loan with Zacatepec in 2019.[8]
On 16 April 2021, Alfaro returned to Major League Soccer, signing with D.C. United.[11] The next day, Alfaro debuted for the team in the 2–1 win over New York City FC.[12] Alfaro scored his first MLS career goal on 1 May 2021, in a 1–4 loss against the San Jose Earthquakes.[13] Following the 2022 season, his contract option was declined by D.C. United.[14]
New York City FC
On 22 December 2022, Alfaro signed a contract through 2023, with an option to extend for the 2024 Major League Soccer season with New York City FC.
LA Galaxy
Alfaro was traded to MLS side LA Galaxy on 11 July 2023 in exchange for $125,000 of General Allocation Money.[15]