SRP is a type of password-authenticated key exchange (PAKE) that has a couple of excellent features for authentication.
It is used by 1Password, iCloud, AWS Cognito and more for login authentication.
The kind lads over at 1Password provided the following rationale for using SRP:
This implementation of the SRP-6a protocol requires just two API calls:
A B-first implementation of the SRP protocol reveals the public value B to the client before receiving the client's public value A and message. This is slightly different than Tom's pysrp, allowing for a different data flow. This flow is optimized for cloud-native APIs.