core: fix source_flow_manager throwing error when authenticated user attempts to re-authenticate with existing link #25918

Job	Run time
lint-golint	38s
test-unittest	3m 1s
ci-outpost-mark	1s
build-binary (proxy, linux, amd64)	1m 54s
build-container (proxy)	2m 25s
build-binary (proxy, linux, arm64)	1m 59s
build-container (ldap)	2m 24s
build-binary (ldap, linux, amd64)	1m 45s
build-container (radius)	3m 30s
build-binary (ldap, linux, arm64)	2m 4s
build-container (rac)	2m 39s
build-binary (radius, linux, amd64)	2m 0s
build-binary (radius, linux, arm64)	1m 57s
build-binary (rac, linux, amd64)	1m 45s
build-binary (rac, linux, arm64)	1m 57s
	29m 59s

Provide feedback