Integrated Windows Authentication / Kerberos gives the end-user access to Atlassian products without entering a username or password. It is typically used in an enterprise LAN and is the preferred choice for Windows domains and Microsoft Desktop environments.
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It is perfectly fine to combine IWA with other SSO mechanisms such as SAML or OpenID Connect (OIDC). In such a combination, IWA provides hassle-free login experiences when the user is present at his desktop machine on in the office, while SAML / OIDC enables the user to log in when they are on the run go outside the office or when accessing from cellphones or other non-Kerberos compatible devices.
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Kantega SSO Enterprise for Bitbucket allows you to utilize the Kerberos protocol to both authenticate users logging into Bitbucket as well as to authenticate their Git commands.