rahulk.s
Why would SP collect User Credentials and pass it over the wire (internet) from SP Organization to IdP Organization? Don't you think it is a better solution (norm) for IdP to challenge and ask for Credentials.
Where is the User Repository where this Credential is stored. Since IdP is going to authenticate the credentials; the users Identity Info is owned and managed by IdP Organization. The SP has no rights to ask the User for entering their IdP credentials on SP Side. I would be surprised if the IdP Organization even agreed to this and then use SAML as a channel to do it.
Please follow SAML Standards and do not devise such custom solution which fits no Standards OR no Specifications. I would recommend revisiting the design and chalking out what is really needed to achieve SSO.
Alternatively, if you could suggest the reasoning behind adopting such a wayward approach, it may be helpful to try and understand WHY?
Regards
Hubert