USE master; 

SELECT SUSER_NAME(principal_id) AS endpoint_owner ,name AS endpoint_name

FROM sys.database_mirroring_endpoints; 

SELECT EPS.name, SPS.STATE, CONVERT(nvarchar(38), SUSER_NAME(SPS.grantor_principal_id))AS [GRANTED BY], SPS.TYPE AS PERMISSION, CONVERT(nvarchar(46),SUSER_NAME(SPS.grantee_principal_id))AS [GRANTED TO]

FROM sys.server_permissions SPS , sys.endpoints EPS WHERE SPS.major_id = EPS.endpoint_id AND name = 'Hadr_endpoint'

ORDER BY Permission,[GRANTED BY], [GRANTED TO];

BEGIN TRAN

USE master; 

ALTER AUTHORIZATION ON ENDPOINT::Hadr_endpoint TO sa;  

GRANT CONNECT ON ENDPOINT::Hadr_endpoint TO [SQL Login 1];

GRANT CONNECT ON ENDPOINT::Hadr_endpoint TO [SQL Login 2]; 

COMMIT