From BOL:
Permissions
Requires ALTER ANY CREDENTIAL permission to create or modify a credential and ALTER ANY LOGIN permission to map a login to a credential.
Also from BOL:
Members of the securityadmin fixed server role manage logins and their properties. They can GRANT, DENY, and REVOKE server-level permissions. They can also GRANT, DENY, and REVOKE database-level permissions if they have access to a database. Additionally, they can reset passwords for SQL Server logins.
And this from 2008 R2 BOL (they don't have an updated version of this article):
securityadmin - ALTER ANY LOGIN
Jack Corbett
Consultant - Straight Path Solutions
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