Authenticating users from external website using Active Directory

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I have an external web site (running TomCat 5) for our school that has a
faculty and student access area. We want this area to be password protected
using student or faculty AD credentials so our users don't have to know
multiple account information. Our web designer is trying to use Open LDAP to
make a connection and verify whether a user is valid or not. However, this
constantly gives us errors as follows:

Error: LDAPException: Operations Error (1) Operations Error
LDAPException: Server Message: 00000000: LdapErr: DSID-0C090B95, comment: In
order to perform this operation a successful bind must be completed on the
connection., data 0, vece
LDAPException: Matched DN:

And:

Error: LDAPException: Invalid Credentials (49) Invalid Credentials
LDAPException: Server Message: 80090308: LdapErr: DSID-0C090334, comment:
AcceptSecurityContext error, data 525, vece
LDAPException: Matched DN:

Does any one know of a secure way to achieve our goal? The whole site is
database driven as well and has a customized web interface.

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