@nicomilie: Are you asking where to find this value? If so, you can use the GET users/show endpoint. Look for the id_str attribute. See the following example:
$ twurl -H api.twitter.com "/1.1/users/show.json?screen_name=twitterdev" | jq
{
"id": 2244994945,
"id_str": "2244994945",
"name": "TwitterDev",
"screen_name": "TwitterDev",
"location": "Internet",
"profile_location": null,
"description": "Developer and Platform Relations @Twitter. We are developer advocates. We can't answer all your questions, but we listen to all of them!",
"url": "https://t.co/66w26cua1O",
"entities": {
"url": {
"urls": [
{
"url": "https://t.co/66w26cua1O",
"expanded_url": "https://dev.twitter.com/",
"display_url": "dev.twitter.com",
"indices": [
0,
23
]
}
]
},
"description": {
"urls": []
}
},
"protected": false,
"followers_count": 437141,
"friends_count": 1535,
"listed_count": 1045,
"created_at": "Sat Dec 14 04:35:55 +0000 2013",
"favourites_count": 1887,
"utc_offset": -25200,
"time_zone": "Pacific Time (US & Canada)",
"geo_enabled": true,
"verified": true,
"statuses_count": 2796,
"lang": "en",
"status": ...,
"contributors_enabled": false,
"is_translator": false,
"is_translation_enabled": false,
"profile_background_color": "FFFFFF",
"profile_background_image_url": "http://abs.twimg.com/images/themes/theme1/bg.png",
"profile_background_image_url_https": "https://abs.twimg.com/images/themes/theme1/bg.png",
"profile_background_tile": false,
"profile_image_url": "http://pbs.twimg.com/profile_images/530814764687949824/npQQVkq8_normal.png",
"profile_image_url_https": "https://pbs.twimg.com/profile_images/530814764687949824/npQQVkq8_normal.png",
"profile_banner_url": "https://pbs.twimg.com/profile_banners/2244994945/1396995246",
"profile_link_color": "0084B4",
"profile_sidebar_border_color": "FFFFFF",
"profile_sidebar_fill_color": "DDEEF6",
"profile_text_color": "333333",
"profile_use_background_image": false,
"has_extended_profile": false,
"default_profile": false,
"default_profile_image": false,
"following": true,
"follow_request_sent": false,
"notifications": false,
"translator_type": "regular"
}
You need to use this value with the as_user_id parameter if creating Tweets on behalf of another user (as long as the user you’re trying to Tweet as has given you permission to do so).