public async Task <string> GetAuthorizationUrlAsync()
{
RequestGuid guid = new RequestGuid();
string guidString = guid.ToString();
Dictionary <string, string> query = new Dictionary <string, string>
{
{ "client_id", OAUTH_CLIENT_ID },
{ "response_type", "code" },
{ "state", guidString },
{ "redirect_uri", REDIRECT_URI },
};
HttpResponseMessage response = await _client.GetAsync(QueryHelpers.AddQueryString(AUTH_URI, query));
/* URI is encoded twice, so need to decode twice to get the query string */
string firstDecode = WebUtility.UrlDecode(response.RequestMessage.RequestUri.ToString());
string resultUri = WebUtility.UrlDecode(firstDecode);
int queryIndex = resultUri.IndexOf('?');
if (queryIndex < 0)
{
throw new InvalidQueryException("No query string returned by authorization request.");
}
Dictionary <string, StringValues> queryValues = QueryHelpers.ParseNullableQuery(resultUri.Substring(queryIndex));
if (queryValues == null)
{
throw new InvalidQueryException("Invalid query string returned by authorization request.");
}
string stateReturned = queryValues["state"];
if (stateReturned != guidString)
{
throw new InvalidOperationException("Incorrect state returned by authorization request.");
}
/* Request for authorization URL was successful */
_authMgr.AddRequestGuid(guid);
return(response.RequestMessage.RequestUri.ToString());
}