sasl_client_start() selects a mechanism for authentication and starts the authentication
session. The mechlist is the list of mechanisms the client might like
to use. The mechanisms in the list are not necessarily supported by
the client or even valid. SASL determines which of these to use based
upon the security preferences specified earlier. The list of
mechanisms is typically a list of mechanisms the server supports
acquired from a capability request.
If SASL_INTERACT is returned the library needs some values to be
filled in before it can proceed. The prompt_need structure will be
filled in with requests. The application should fulfill these requests
and call sasl_client_start again with identical parameters (the
prompt_need parameter will be the same pointer as before but filled in
by the application).
mechlist is a list of mechanisms the server has available. Punctuation is ignored.
prompt_need is filled in with a list of prompts needed to continue (if necessary).
clientoutlen is created. It is the initial client response to send to the
server. It is the job of the
client to send it over the network to the server.
Any protocol specific encoding (such as base64
encoding) necessary needs to be done by the client.
If the protocol lacks client-send-first capability, then set
clientout to NULL.
If there is no initial client-send, then
*clientout will be set to NULL on return.
mech contains the name of the chosen SASL mechanism (on success)