The gss_accept_sec_context() function allows a remotely initiated security context between the application and a remote peer to be established. The routine may return an output_token, which should be transferred to the peer application, where the peer application will present it to gss_init_sec_context(). See gss_init_sec_context(3GSS). If no token need be sent, gss_accept_sec_context() will indicate this by setting the length field of the output_token argument to zero. To complete the context establishment, one or more reply tokens may be required from the peer application; if so, gss_accept_sec_context() will return a status flag of GSS_S_CONTINUE_NEEDED, in which case it should be called again when the reply token is received from the peer application, passing the token to gss_accept_sec_context() by means of the input_token parameters.

Portable applications should be constructed to use the token length and return status to determine whether to send or to wait for a token.

Whenever gss_accept_sec_context() returns a major status that includes the value GSS_S_CONTINUE_NEEDED, the context is not fully established and the following restrictions apply to the output parameters:

• The value returned by means of the time_rec parameter is undefined.
• Unless the accompanying ret_flags parameter contains the bit GSS_C_PROT_READY_FLAG, which indicates that per-message services may be applied in advance of a successful completion status, the value returned by the mech_type parameter may be undefined until gss_accept_sec_context() returns a major status value of GSS_S_COMPLETE.

The values of the GSS_C_DELEG_FLAG, GSS_C_MUTUAL_FLAG, GSS_C_REPLAY_FLAG, GSS_C_SEQUENCE_FLAG, GSS_C_CONF_FLAG, GSS_C_INTEG_FLAG and GSS_C_ANON_FLAG bits returned by means of the ret_flags parameter are values that would be valid if context establishment were to succeed.

The values of the GSS_C_PROT_READY_FLAG and GSS_C_TRANS_FLAG bits within ret_flags indicate the actual state at the time gss_accept_sec_context() returns, whether or not the context is fully established. However, applications should not rely on this behavior, as GSS_C_PROT_READY_FLAG was not defined in Version 1 of the GSS-API. Instead, applications should be prepared to use per-message services after a successful context establishment, based upon the GSS_C_INTEG_FLAG and GSS_C_CONF_FLAG values.

All other bits within the ret_flags argument are set to zero.

While gss_accept_sec_context() returns GSS_S_CONTINUE_NEEDED, the values returned by means of the the ret_flags argument indicate the services available from the established context. If the initial call of gss_accept_sec_context() fails, no context object is created, and the value of the context_handle parameter is set to GSS_C_NO_CONTEXT. In the event of a failure on a subsequent call, the security context and the context_handle parameter are left untouched for the application to delete using gss_delete_sec_context(3GSS). During context establishment, the informational status bits GSS_S_OLD_TOKEN and GSS_S_DUPLICATE_TOKEN indicate fatal errors; GSS-API mechanisms always return them in association with a routine error of GSS_S_FAILURE. This pairing requirement did not exist in version 1 of the GSS-API specification, so applications that wish to run over version 1 implementations must special-case these codes.

The parameter descriptions for gss_accept_sec_context() follow:

minor_status

The status code returned by the underlying mechanism.

context_handle

The context handle to return to the initiator. This should be set to GSS_C_NO_CONTEXT before the loop begins.

acceptor_cred_handle

The handle for the credentials acquired by the acceptor, typically through gss_acquire_cred(). It may be initialized to GSS_C_NO_CREDENTIAL to indicate a default credential to use. If no default credential is defined, the function returns GSS_C_NO_CRED.

input_token_buffer

Token received from the context initiative.

input_chan_bindings

Optional application-specified bindings. Allows application to securely bind channel identification information to the security context. Set to GSS_C_NO_CHANNEL_BINDINGS if you do not want to use channel bindings.

src_name

The authenticated name of the context initiator. After use, this name should be deallocated by passing it to gss_release_name(). See gss_release_name(3GSS). If not required, specify NULL.

mech_type

The security mechanism used. Set to NULL if it does not matter which mechanism is used.

output_token

The token to send to the acceptor. Initialize it to GSS_C_NO_BUFFER before the function is called (or its length field set to zero). If the length is zero, no token need be sent.

ret_flags

Contains various independent flags, each of which indicates that the context supports a specific service option. If not needed, specify NULL. Test the returned bit-mask ret_flags value against its symbolic name to determine if the given option is supported by the context. ret_flags may contain one of the following values:

GSS_C_DELEG_FLAG

If true, delegated credentials are available by means of the delegated_cred_handle parameter. If false, no credentials were delegated.

GSS_C_MUTUAL_FLAG

If true, a remote peer asked for mutual authentication. If false, no remote peer asked for mutual authentication.

GSS_C_REPLY_FLAG

If true, replay of protected messages will be detected. If false, replayed messages will not be detected.

GSS_C_SEQUENCE_FLAG

If true, out of sequence protected messages will be detected. If false, they will not be detected.

GSS_C_CONF_FLAG

If true, confidentiality service may be invoked by calling the gss_wrap() routine. If false, no confidentiality service is available by means of gss_wrap(). gss_wrap() will provide message encapsulation, data-origin authentication and integrity services only.

GSS_C_INTEG_FLAG

If true, integrity service may be invoked by calling either the gss_get_mic(3GSS) or the gss_wrap(3GSS) routine. If false, per-message integrity service is not available.

GSS_C_ANON_FLAG

If true, the initiator does not wish to be authenticated. The src_name parameter, if requested, contains an anonymous internal name. If false, the initiator has been authenticated normally.

GSS_C_PROT_READY_FLAG

If true, the protection services specified by the states of GSS_C_CONF_FLAG and GSS_C_INTEG_FLAG are available if the accompanying major status return value is either GSS_S_COMPLETE or GSS_S_CONTINUE_NEEDED. If false, the protection services are available only if the accompanying major status return value is GSS_S_COMPLETE.

GSS_C_TRANS_FLAG

If true, the resultant security context may be transferred to other processes by means of a call to gss_export_sec_context(3GSS). If false, the security context cannot be transferred.

time_rec

The number of sections for which the context will remain value Specify NULL if not required.

delegated_cred_handle

The credential value for credentials received from the context's initiator. It is valid only if the initiator has requested that the acceptor act as a proxy: that is, if the ret_flag argument resolves to GSS_C_DELEG_FLAG.

gss_accept_sec_context() may return the following status codes:

GSS_S_COMPLETE

Successful completion.

GSS_S_CONTINUE_NEEDED

A token from the peer application is required to complete the context, and that gss_accept_sec_context() must be called again with that token.

GSS_S_DEFECTIVE_TOKEN

Consistency checks performed on the input_token failed.

GSS_S_DEFECTIVE_CREDENTIAL

Consistency checks performed on the credential failed.

GSS_S_NO_CRED

The supplied credentials were not valid for context acceptance, or the credential handle did not reference any credentials.

GSS_S_CREDENTIALS_EXPIRED

The referenced credentials have expired.

GSS_S_BAD_BINDINGS

The input_token contains different channel bindings than those specified by means of the input_chan_bindings parameter.

GSS_S_NO_CONTEXT

The supplied context handle did not refer to a valid context.

GSS_S_BAD_SIG

The input_token contains an invalid MIC.

GSS_S_OLD_TOKEN

The input_token was too old. This is a fatal error while establishing context.

GSS_S_DUPLICATE_TOKEN

The input_token is valid, but it is duplicate of a token already processed. This is a fatal error while establishing context.

GSS_S_BAD_MECH

The token received specified a mechanism that is not supported by the implementation or the provided credential.

GSS_S_FAILURE

The underlying mechanism detected an error for which no specific GSS status code is defined. The mechanism-specific status code reported by means of the minor_status parameter details the error condition.

See attributes(5) for descriptions of the following attributes:

gss_delete_sec_context(3GSS), gss_export_sec_context(3GSS), gss_get_mic(3GSS), gss_init_sec_context(3GSS), gss_release_name(3GSS), gss_wrap(3GSS), attributes(5)

GSS-API Programming Guide