pEpEngine/src/keymanagement.c

// This file is under GNU General Public License 3.0
// see LICENSE.txt

#include "platform.h"

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <ctype.h>

#include "pEp_internal.h"
#include "keymanagement.h"
#include "KeySync_fsm.h"

#include "blacklist.h"

static bool key_matches_address(PEP_SESSION session, const char* address,
                                const char* fpr) {
    if (!session || !address || !fpr)
        return false;
    
    bool retval = false;
    stringlist_t *keylist = NULL;
    PEP_STATUS status = find_keys(session, address, &keylist);
    if (status == PEP_STATUS_OK && keylist) {
        stringlist_t* curr = keylist;
        while (curr) {
            if (curr->value) {
                if (strcasecmp(curr->value, fpr)) {
                    retval = true;
                    break;
                }
            }
            curr = curr->next;
        }
    }
    
    free_stringlist(keylist);
    return retval;                             
}

// Does not return PASSPHRASE errors
PEP_STATUS elect_pubkey(
        PEP_SESSION session, pEp_identity * identity, bool check_blacklist
    )
{
    PEP_STATUS status;
    stringlist_t *keylist = NULL;
    char *_fpr = "";
    identity->comm_type = PEP_ct_unknown;

    status = find_keys(session, identity->address, &keylist);
    assert(status != PEP_OUT_OF_MEMORY);
    if (status == PEP_OUT_OF_MEMORY)
        return PEP_OUT_OF_MEMORY;
    
    if (!keylist || !keylist->value)
        identity->comm_type = PEP_ct_key_not_found;    
    else {
        stringlist_t *_keylist;
        for (_keylist = keylist; _keylist && _keylist->value; _keylist = _keylist->next) {
            PEP_comm_type _comm_type_key;

            status = get_key_rating(session, _keylist->value, &_comm_type_key);
            assert(status != PEP_OUT_OF_MEMORY);
            if (status == PEP_OUT_OF_MEMORY) {
                free_stringlist(keylist);
                return PEP_OUT_OF_MEMORY;
            }

            if (_comm_type_key != PEP_ct_compromised &&
                _comm_type_key != PEP_ct_unknown)
            {
                if (identity->comm_type == PEP_ct_unknown ||
                    _comm_type_key > identity->comm_type)
                {
                    bool blacklisted = false;
                    bool mistrusted = false;
                    status = is_mistrusted_key(session, _keylist->value, &mistrusted);
                    if (status == PEP_STATUS_OK && check_blacklist)
                        status = blacklist_is_listed(session, _keylist->value, &blacklisted);
                    if (status == PEP_STATUS_OK && !mistrusted && !blacklisted) {
                        identity->comm_type = _comm_type_key;
                        _fpr = _keylist->value;
                    }
                }
            }
        }
    }
    free(identity->fpr);

    if (!_fpr || _fpr[0] == '\0')
        identity->fpr = NULL;
    else {    
        identity->fpr = strdup(_fpr);
        if (identity->fpr == NULL) {
            free_stringlist(keylist);
            return PEP_OUT_OF_MEMORY;
        }
    }
    
    free_stringlist(keylist);
    return PEP_STATUS_OK;
}


// own_must_contain_private is usually true when calling;
// we only set it to false when we have the idea of
// possibly having an own pubkey that we need to check on its own
// N.B. Checked for PASSPHRASE errors - will now return them always
// False value of "renew_private" prevents their possibility, though.
PEP_STATUS validate_fpr(PEP_SESSION session, 
                        pEp_identity* ident,
                        bool check_blacklist,
                        bool own_must_contain_private,
                        bool renew_private) {
    
    PEP_STATUS status = PEP_STATUS_OK;
    
    if (!session || !ident || !ident->fpr || !ident->fpr[0])
        return PEP_ILLEGAL_VALUE;    
        
    char* fpr = ident->fpr;
    
    bool has_private = false;
    status = contains_priv_key(session, fpr, &has_private);
    
    // N.B. Will not contain PEP_PASSPHRASE related returns here
    if (ident->me && own_must_contain_private) {
        if (status != PEP_STATUS_OK || !has_private)
            return PEP_KEY_UNSUITABLE;
    }
    else if (status != PEP_STATUS_OK && has_private) // should never happen
        has_private = false;
    
    status = get_trust(session, ident);
    if (status != PEP_STATUS_OK)
        ident->comm_type = PEP_ct_unknown;
            
    PEP_comm_type ct = ident->comm_type;

    if (ct == PEP_ct_unknown) {
        // If status is bad, it's ok, we get the rating
        // we should use then (PEP_ct_unknown)
        get_key_rating(session, fpr, &ct);
        ident->comm_type = ct;
    }
    else if (ct == PEP_ct_key_expired || ct == PEP_ct_key_expired_but_confirmed) {
        PEP_comm_type ct_expire_check = PEP_ct_unknown;
        get_key_rating(session, fpr, &ct_expire_check);
        if (ct_expire_check >= PEP_ct_strong_but_unconfirmed) {
            ident->comm_type = ct_expire_check;
            if (ct == PEP_ct_key_expired_but_confirmed)
                ident->comm_type |= PEP_ct_confirmed;
            ct = ident->comm_type;
            // We need to fix this trust in the DB.
            status = set_trust(session, ident);
        }
    }
    
    
    bool pEp_user = false;
    
    is_pEp_user(session, ident, &pEp_user);

    if (pEp_user) {
        switch (ct) {
            case PEP_ct_OpenPGP:
            case PEP_ct_OpenPGP_unconfirmed:
                ct += 0x47; // difference between PEP and OpenPGP values;
                ident->comm_type = ct;
                break;
            default:
                break;
        }
    }
    
    bool revoked, expired;
    bool blacklisted = false;
    
    // Should not need to decrypt key material
    status = key_revoked(session, fpr, &revoked);    
        
    if (status != PEP_STATUS_OK) {
        return status;
    }
    
    if (!revoked) {
        time_t exp_time = (ident->me ? 
                           time(NULL) + (7*24*3600) : time(NULL));

        // Should not need to decrypt key material                           
        status = key_expired(session, fpr, 
                             exp_time,
                             &expired);
        
        assert(status == PEP_STATUS_OK);
        if (status != PEP_STATUS_OK)
            return status;

        if (check_blacklist && IS_PGP_CT(ct) &&
            !ident->me) {
            status = blacklist_is_listed(session, 
                                         fpr, 
                                         &blacklisted);
                                         
            if (status != PEP_STATUS_OK)
                return status;
        }
    }
            
    // Renew key if it's expired, our own, has a private part,
    // isn't too weak, and we didn't say "DON'T DO THIS"
    if (renew_private && ident->me && has_private && 
        (ct >= PEP_ct_strong_but_unconfirmed) && 
        !revoked && expired) {
        // extend key
        timestamp *ts = new_timestamp(time(NULL) + KEY_EXPIRE_DELTA);
        status = renew_key(session, fpr, ts);
        free_timestamp(ts);

        if (status == PEP_PASSPHRASE_REQUIRED || status == PEP_WRONG_PASSPHRASE)
            return status;
            
        if (status == PEP_STATUS_OK) {
            // if key is valid (second check because pEp key might be extended above)
            //      Return fpr        
            status = key_expired(session, fpr, time(NULL), &expired);            
            if (status != PEP_STATUS_OK)
                return status;
                
            if (expired) {
                if (ident->comm_type & PEP_ct_confirmed || (ident->comm_type == PEP_ct_key_expired_but_confirmed))
                    ident->comm_type = PEP_ct_key_expired_but_confirmed;
                else
                    ident->comm_type = PEP_ct_key_expired;
                return status;
            }
            // communicate key(?)
        }        
    }
     
    if (revoked) 
        ct = PEP_ct_key_revoked;
    else if (expired) {
        if (ident->comm_type & PEP_ct_confirmed || (ident->comm_type == PEP_ct_key_expired_but_confirmed))
            ct = PEP_ct_key_expired_but_confirmed;
        else
            ct = PEP_ct_key_expired;
    }
    else if (blacklisted) { // never true for .me
        ident->comm_type = ct = PEP_ct_key_not_found;
        free(ident->fpr);
            ident->fpr = strdup("");
        status = PEP_KEY_BLACKLISTED;
    }
    
    switch (ct) {
        case PEP_ct_key_expired:
        case PEP_ct_key_expired_but_confirmed:
        case PEP_ct_key_revoked:
        case PEP_ct_key_b0rken:
            // delete key from being default key for all users/identities
            status = remove_fpr_as_default(session, fpr);
            status = update_trust_for_fpr(session, 
                                          fpr, 
                                          ct);
        case PEP_ct_mistrusted:                                  
            free(ident->fpr);
            ident->fpr = NULL;
            ident->comm_type = ct;            
            status = PEP_KEY_UNSUITABLE;
        default:
            break;
    }            

    return status;
}

PEP_STATUS get_all_keys_for_user(PEP_SESSION session, 
                                 const char* user_id,
                                 stringlist_t** keys) {

    if (!session || EMPTYSTR(user_id) || !keys)
        return PEP_ILLEGAL_VALUE;
        
    PEP_STATUS status = PEP_STATUS_OK;
        
    *keys = NULL;
    stringlist_t* _kl = NULL;
    
    sqlite3_reset(session->get_all_keys_for_user);
    sqlite3_bind_text(session->get_all_keys_for_user, 1, user_id, -1, SQLITE_STATIC);

    int result = -1;
    
    while ((result = sqlite3_step(session->get_all_keys_for_user)) == SQLITE_ROW) {
        const char* keyres = (const char *) sqlite3_column_text(session->get_all_keys_for_user, 0);
        if (keyres) {
            if (_kl)
                stringlist_add(_kl, keyres);
            else
                _kl = new_stringlist(keyres);
        }
    }
    
    if (!_kl)
        return PEP_KEY_NOT_FOUND;
        
    *keys = _kl;
    
    sqlite3_reset(session->get_all_keys_for_user);

    return status;
}

PEP_STATUS get_user_default_key(PEP_SESSION session, const char* user_id,
                                char** default_key) {
    assert(session);
    assert(user_id);
    
    if (!session || !user_id)
        return PEP_ILLEGAL_VALUE;

    PEP_STATUS status = PEP_STATUS_OK;
            
    // try to get default key for user_data
    sqlite3_reset(session->get_user_default_key);
    sqlite3_bind_text(session->get_user_default_key, 1, user_id, 
                      -1, SQLITE_STATIC);
    
    const int result = sqlite3_step(session->get_user_default_key);
    char* user_fpr = NULL;
    if (result == SQLITE_ROW) {
        const char* u_fpr =
            (char *) sqlite3_column_text(session->get_user_default_key, 0);
        if (u_fpr)
            user_fpr = strdup(u_fpr);
    }
    else
        status = PEP_GET_KEY_FAILED;
        
    sqlite3_reset(session->get_user_default_key);
    
    *default_key = user_fpr;
    return status;     
}

// Only call on retrieval of previously stored identity!
// Also, we presume that if the stored_identity was sent in
// without an fpr, there wasn't one in the trust DB for this
// identity.
//
// Will now NOT return passphrase errors, as we tell 
// validate_fpr NOT to renew it. And we specifically suppress them 
// with "PEP_KEY_UNSUITABLE"
//
PEP_STATUS get_valid_pubkey(PEP_SESSION session,
                         pEp_identity* stored_identity,
                         bool* is_identity_default,
                         bool* is_user_default,
                         bool* is_address_default,
                         bool check_blacklist) {
    
    PEP_STATUS status = PEP_STATUS_OK;

    if (!stored_identity || EMPTYSTR(stored_identity->user_id)
        || !is_identity_default || !is_user_default || !is_address_default)
        return PEP_ILLEGAL_VALUE;
        
    *is_identity_default = *is_user_default = *is_address_default = false;

    PEP_comm_type first_reject_comm_type = PEP_ct_key_not_found;
    PEP_STATUS first_reject_status = PEP_KEY_NOT_FOUND;
    
    char* stored_fpr = stored_identity->fpr;
    
    // Input: stored identity retrieved from database
    // if stored identity contains a default key; if so, we return from here
    if (!EMPTYSTR(stored_fpr)) {
        
        // Won't ask for passphrase, won't return PASSPHRASE status
        // Because of non-renewal
        status = validate_fpr(session, stored_identity, check_blacklist, true, false);
        switch (status) {
            case PEP_STATUS_OK:
                if (!EMPTYSTR(stored_identity->fpr)) {
                    *is_identity_default = *is_address_default = true;
                    return status;                    
                }
                break;
            case PEP_KEY_NOT_FOUND:
                break;
            default:    
                first_reject_status = status;
                first_reject_comm_type = stored_identity->comm_type;            
        }    
    } 
    // if no valid default stored identity key found
    free(stored_identity->fpr);
    stored_identity->fpr = NULL;
    
    char* user_fpr = NULL;
    status = get_user_default_key(session, stored_identity->user_id, &user_fpr);
    
    if (!EMPTYSTR(user_fpr)) {             
        // There exists a default key for user, so validate
        stored_identity->fpr = user_fpr;
        
        // Won't ask for passphrase, won't return PASSPHRASE status
        // Because of non-renewal
        status = validate_fpr(session, stored_identity, check_blacklist, true, false);

        switch (status) {
            case PEP_STATUS_OK:
                if (!EMPTYSTR(stored_identity->fpr)) {
                    *is_user_default = true;
                    *is_address_default = key_matches_address(session, 
                                                              stored_identity->address,
                                                              stored_identity->fpr);
                    return status;
                }
                break;
            case PEP_KEY_NOT_FOUND:
                break;
            default: 
                if (first_reject_status != PEP_KEY_NOT_FOUND) {
                    first_reject_status = status;
                    first_reject_comm_type = stored_identity->comm_type;            
                }    
        }    
    }

    // If we got here, there's no usable default.
    
    // status = elect_pubkey(session, stored_identity, check_blacklist);
    // if (status == PEP_STATUS_OK) {
    //     if (!EMPTYSTR(stored_identity->fpr)) {
    //         // Won't ask for passphrase, won't return PASSPHRASE status
    //         // Because of non-renewal            
    //         status = validate_fpr(session, stored_identity, false, true, false); // blacklist already filtered of needed
    //     }    
    // }    
    // else if (status != PEP_KEY_NOT_FOUND && first_reject_status != PEP_KEY_NOT_FOUND) {
    //     first_reject_status = status;
    //     first_reject_comm_type = stored_identity->comm_type;
    // }
    
    switch (first_reject_comm_type) {
        case PEP_ct_key_revoked:
        case PEP_ct_key_b0rken:
        case PEP_ct_key_expired:
        case PEP_ct_key_expired_but_confirmed:
        case PEP_ct_compromised:
        case PEP_ct_mistrusted:
            // this only happens when it's all there is
            status = first_reject_status;
            free(stored_identity->fpr);
            stored_identity->fpr = NULL;
            stored_identity->comm_type = first_reject_comm_type;
            break;    
        default:
            if (check_blacklist && status == PEP_KEY_BLACKLISTED) {
                free(stored_identity->fpr);
                stored_identity->fpr = NULL;
                stored_identity->comm_type = PEP_ct_key_not_found;
            }
            break;
    }
    
    // should never happen, but we will MAKE sure
    if (PASS_ERROR(status)) 
        status = PEP_KEY_UNSUITABLE; // renew it on your own time, baby
        
    return status;
}

static void transfer_ident_lang_and_flags(pEp_identity* new_ident,
                                          pEp_identity* stored_ident) {
    if (new_ident->lang[0] == 0) {
      new_ident->lang[0] = stored_ident->lang[0];
      new_ident->lang[1] = stored_ident->lang[1];
      new_ident->lang[2] = 0;
    }

    new_ident->flags = stored_ident->flags;
    new_ident->me = new_ident->me || stored_ident->me;
}

static void adjust_pEp_trust_status(PEP_SESSION session, pEp_identity* identity) {
    assert(session);
    assert(identity);
    
    if (identity->comm_type < PEP_ct_strong_but_unconfirmed ||
        (identity->comm_type | PEP_ct_confirmed) == PEP_ct_pEp)
        return;
    
    bool pEp_user;
    
    is_pEp_user(session, identity, &pEp_user);
    
    if (pEp_user) {
        PEP_comm_type confirmation_status = identity->comm_type & PEP_ct_confirmed;
        identity->comm_type = PEP_ct_pEp_unconfirmed | confirmation_status;
        if (identity->major_ver == 0) {
            identity->major_ver = 2;
            identity->minor_ver = 0;
        }    
    }
}


// NEVER called on an own identity. 
// But we also make sure get_valid_pubkey 
// and friends NEVER return with a password error.
// (get_valid_pubkey tells validate_fpr not to try renewal)
// Will not return PASSPHRASE errors.
static PEP_STATUS prepare_updated_identity(PEP_SESSION session,
                                                 pEp_identity* return_id,
                                                 pEp_identity* stored_ident,
                                                 bool store) {
    
    if (!session || !return_id || !stored_ident)
        return PEP_ILLEGAL_VALUE;
    
    PEP_STATUS status;
    
    bool is_identity_default, is_user_default, is_address_default;
    bool no_stored_default = EMPTYSTR(stored_ident->fpr);
    
    status = get_valid_pubkey(session, stored_ident,
                                &is_identity_default,
                                &is_user_default,
                                &is_address_default,
                                false);
        
    switch (status) {
        case PEP_STATUS_OK:
            if (!EMPTYSTR(stored_ident->fpr)) {
                // set identity comm_type from trust db (user_id, FPR)
                status = get_trust(session, stored_ident);
                if (status == PEP_CANNOT_FIND_IDENTITY || stored_ident->comm_type == PEP_ct_unknown) {
                    // This is OK - there is no trust DB entry, but we
                    // found a key. We won't store this, but we'll
                    // use it.
                    PEP_comm_type ct = PEP_ct_unknown;
                    status = get_key_rating(session, stored_ident->fpr, &ct);
                    stored_ident->comm_type = ct;
                }
            }
            else if (stored_ident->comm_type == PEP_ct_unknown)
                stored_ident->comm_type = PEP_ct_key_not_found;
            break;    
        default:    
            free(stored_ident->fpr);
            stored_ident->fpr = NULL;
            stored_ident->comm_type = PEP_ct_key_not_found;        
    }

    free(return_id->fpr);
    return_id->fpr = NULL;
    if (status == PEP_STATUS_OK && !EMPTYSTR(stored_ident->fpr))
        return_id->fpr = strdup(stored_ident->fpr);
        
    return_id->comm_type = stored_ident->comm_type;
                    
    // We patch the DB with the input username, but if we didn't have
    // one, we pull it out of storage if available.
    if (!EMPTYSTR(stored_ident->username)) {
        if (!EMPTYSTR(return_id->username) && 
            (strcasecmp(return_id->username, return_id->address) == 0)) {
            free(return_id->username);
            return_id->username = NULL;
        }
        if (EMPTYSTR(return_id->username)) {
            free(return_id->username);
            return_id->username = strdup(stored_ident->username);
        }
    }
    else {
        if (EMPTYSTR(return_id->username))
            return_id->username = strdup(return_id->address);
    }
    
    return_id->me = stored_ident->me;
    
    return_id->major_ver = stored_ident->major_ver;
    return_id->minor_ver = stored_ident->minor_ver;

    // FIXME: Do we ALWAYS do this? We probably should...
    if (EMPTYSTR(return_id->user_id)) {
        free(return_id->user_id);
        return_id->user_id = strdup(stored_ident->user_id);
    } 
    
    adjust_pEp_trust_status(session, return_id);
   
    // Call set_identity() to store
    if ((is_identity_default || is_user_default) &&
         is_address_default) {                 
         // if we got an fpr which is default for either user
         // or identity AND is valid for this address, set in DB
         // as default
         status = set_identity(session, return_id);
    } 
    else if (no_stored_default && !EMPTYSTR(return_id->fpr) 
             && return_id->comm_type != PEP_ct_key_revoked
             && return_id->comm_type != PEP_ct_key_expired
             && return_id->comm_type != PEP_ct_key_expired_but_confirmed
             && return_id->comm_type != PEP_ct_mistrusted 
             && return_id->comm_type != PEP_ct_key_b0rken) { 
        // We would have stored this anyway for a first-time elected key. We just have an ident w/ no default already.
        status = set_identity(session, return_id);
    }
    else { // this is a key other than the default, but there IS a default (FIXME: fdik, do we really want behaviour below?)
        // Store without default fpr/ct, but return the fpr and ct 
        // for current use
        char* save_fpr = return_id->fpr;
        PEP_comm_type save_ct = return_id->comm_type;
        return_id->fpr = NULL;
        return_id->comm_type = PEP_ct_unknown;
        PEP_STATUS save_status = status;
        status = set_identity(session, return_id);
        if (save_status != PEP_STATUS_OK)
            status = save_status;
        return_id->fpr = save_fpr;
        return_id->comm_type = save_ct;
    }
    
    transfer_ident_lang_and_flags(return_id, stored_ident);
    return_id->enc_format = stored_ident->enc_format;    
        
    if (return_id->comm_type == PEP_ct_unknown)
        return_id->comm_type = PEP_ct_key_not_found;
    
    return status;
}

// Should not return PASSPHRASE errors because we force 
// calls that can cause key renewal not to.
DYNAMIC_API PEP_STATUS update_identity(
        PEP_SESSION session, pEp_identity * identity
    )
{
    PEP_STATUS status = PEP_STATUS_OK;

    assert(session);
    assert(identity);
    assert(!EMPTYSTR(identity->address));

    if (!(session && identity && !EMPTYSTR(identity->address)))
        return PEP_ILLEGAL_VALUE;

    //
    // Record some information about the input identity so that we don't keep 
    // evaluating it
    bool is_own_user = identity->me;    
    bool input_has_user_id = !EMPTYSTR(identity->user_id);
    bool input_has_username = !EMPTYSTR(identity->username);
    bool input_has_real_id = input_has_user_id ? (strstr(identity->user_id, "TOFU_") != identity->user_id) : false;

    char* default_own_id = NULL;
    pEp_identity* stored_ident = NULL;

    status = get_default_own_userid(session, &default_own_id);    
    if (status == PEP_STATUS_OK || status == PEP_CANNOT_FIND_IDENTITY)
        status = PEP_STATUS_OK;
    else
        goto pEp_free;        

    // To be clear, if an own identity comes in here, the only way we will accept 
    // it is if the caller did not KNOW this, as indicated by the lack of a known 
    // own user_id and identity->me being false.
    // 
    // IF either of these are set, then the call will fail. If, however, we get
    // an identity which simply has the own address on it, we'll kindly call a read-only
    // version of myself.
    if (!is_own_user) {
        if (default_own_id) {
            if (input_has_user_id) {
                if (strcmp(default_own_id, identity->user_id) == 0) {
                    is_own_user = true;
                }
                else {
                    char* alias = NULL;
                    if (get_userid_alias_default(session, identity->user_id, &alias) == PEP_STATUS_OK) {
                        if (alias && strcmp(default_own_id, alias) == 0)
                            is_own_user = true;
                        free(alias);    
                    }
                }
            }
            else {
                // Check if own address. For now, this is a special case;
                // we try to require apps to send in user_ids, but must prevent
                // writes to an own identity from within THIS function
                // NOTE: These semantics MAY CHANGE.
                bool _own_addr = false;
                is_own_address(session, identity->address, &_own_addr);
                
                if (_own_addr) {
                    free(identity->user_id);
                    identity->user_id = strdup(default_own_id);
                    // Do not renew, do not generate
                    return _myself(session, identity, false, false, false, true);
                }    
            }
        }
        // Otherwise, we don't even HAVE an own user yet, so we're ok.
    }    
    if (is_own_user) {
        free(default_own_id);
        return PEP_ILLEGAL_VALUE;
    }

    // We have, at least, an address.
    // Retrieve stored identity information!    

    //////////////////////////////////////////////////////////////////////////////////////////////////////
    // If we can get a starting identity from the database, do it. If we have a user_id (thank you, users),
    // this is pretty simple.
    // 
    // Otherwise, we double-check that someone didn't pass in an own address (hey, if you don't give us a
    // user_id, we're have to guess somehow, and treating own identities like partner identities is dangerous).
    //////////////////////////////////////////////////////////////////////////////////////////////////////

    if (input_has_user_id) {            
        // (we're gonna update the trust/fpr anyway, so we use the no-fpr-from-trust-db variant)
        //      * do get_identity() to retrieve stored identity information
        status = get_identity_without_trust_check(session, identity->address, identity->user_id, &stored_ident);
    }
    else { // see if we perhaps own this user
        if (default_own_id) {
            status = get_identity(session, 
                                  identity->address, 
                                  default_own_id, 
                                  &stored_ident);
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////////////////
    // If we're unable to get a starting stored ID, we now need to try to get IDs which match the address.
    // Should we find them, we go through the list and try to find an acceptable one by evaluating the 
    // following properties (not in order of priority, and not for every case - the logic here is a mess):
    //
    // 1. Did the input have a user_id?
    // 2. Did the input hava a username?
    // 3. Is the input user_id a real id?
    // 4. Is the stored user_id a real id?
    // 5. Does the stored user_id have a username?
    // 6. Do the names match?
    //
    // Based on this, if we find an acceptable candidate, we do one:
    //
    // 1. Replace the global DB user_id with the input user_id and patch the stored identity's user_id 
    //    (this may be different than 1, though in practice it seems we always do both)
    // 2. Patch the output identity's user_id from the stored identity
    //
    // If we find none, in the case if the has-username-but-no-user_id input case, we'll try a TOFU id
    // fetch before giving up on stored identity candidates.
    //
    // Acceptable candidates are then passed to prepare_update_identity which will patch usernames and
    // find any applicable keys.
    //
    // Unacceptable candidates will then have minimal record information entered depending on how much 
    // came in in the input, TOFU user_ids created when needed, and a new record placed in the DB
    // accordingly.
    //
    if (!stored_ident) {