There is no "legal" way to get this data. This is how I do that:
GET this endpoint. It used for Binance SPA and does not mention in their documentation. Data is an array that contains all trading Binance pairs. For example:
"s":"BTCUSDT", 
"st":"TRADING", 
"b":"BTC", 
"q":"USDT", 
"ba":"฿", 
"a":"", 
"I":"0.00000100", 
"ts":"0.01", 
"an":"Bitcoin", 
"qn":"TetherUS", 
"o":"46915.84", 
"h":"47499.43", 
"l":"44961.09", 
"c":"46791.85", 
"v":"91500.82", 
"qv":"4248420233.17226301", 
"y":0, "as":91500.81462400, 
"pm":"FIAT", "pn":"FIAT", 
"cs":18620881, 
"tags":["pow","mining-zone"], 
"pom":false, 
"pomt":null, 
"etf":false
You need to take the field CS and multiply it by the current asset price. In this case, it will be field C
18620881 * 46791.85 = 871,305M
So this is the current BTC market cap