public async Task AcquireTokenAsync()

in src/Microsoft.Atlas.CommandLine/OAuth2/TokenProvider.cs [31:105]
64 lines of code
15 McCabe index (conditional complexity)

        public async Task<AuthenticationHeaderValue> AcquireTokenAsync(HttpAuthentication auth)
        {
            var tenant = auth.tenant;
            var resourceId = auth.resourceId;
            var clientId = auth.clientId;

            // https://login.microsoftonline.com
            // https://login.windows.net
            var authority = $"https://login.windows.net/{tenant ?? "common"}";

            AccountEntry account = null;
            if (account == null)
            {
                account = _settings.accounts.Where(entry => string.Equals(entry.authority, authority, StringComparison.Ordinal) && string.Equals(entry.resource, resourceId, StringComparison.Ordinal)).LastOrDefault();
            }

            if (account == null)
            {
                account = _settings.accounts.Where(entry => string.IsNullOrEmpty(entry.authority) && string.Equals(entry.resource, resourceId, StringComparison.Ordinal)).LastOrDefault();
            }

            if (account == null)
            {
                account = _settings.accounts.Where(entry => string.Equals(entry.authority, authority, StringComparison.Ordinal) && string.IsNullOrEmpty(entry.resource)).LastOrDefault();
            }

            if (account == null)
            {
                account = _settings.accounts.Where(entry => string.IsNullOrEmpty(entry.authority) && string.IsNullOrEmpty(entry.resource)).LastOrDefault();
            }

            var ctx = new AuthenticationContext(authority, _tokenCache);
            AuthenticationResult result = null;

            if (account != null)
            {
                if (!string.IsNullOrEmpty(account.token))
                {
                    return new AuthenticationHeaderValue("Bearer", account.token);
                }
                else if (!string.IsNullOrEmpty(account.password))
                {
                    var basic = $"{account.username}:{account.password}";
                    return new AuthenticationHeaderValue("Basic", Convert.ToBase64String(Encoding.ASCII.GetBytes(basic)));
                }
                else if (!string.IsNullOrEmpty(account.appid))
                {
                    result = await ctx.AcquireTokenAsync(resourceId, new ClientCredential(account.appid, account.secret));
                }
                else
                {
                    throw new InvalidOperationException("Account entry requires either token or appid and secret values.");
                }
            }
            else
            {
                if (auth.interactive == false)
                {
                    throw new InvalidOperationException("Matching account credentials have not been stored, and interactive authentication is disallowed.");
                }

                try
                {
                    result = await ctx.AcquireTokenSilentAsync(resourceId, clientId);
                }
                catch
                {
                    DeviceCodeResult codeResult = await ctx.AcquireDeviceCodeAsync(resourceId, clientId);
                    _console.Error.WriteLine(codeResult.Message.Color(ConsoleColor.DarkYellow));
                    result = await ctx.AcquireTokenByDeviceCodeAsync(codeResult);
                }
            }

            return new AuthenticationHeaderValue(result.AccessTokenType, result.AccessToken);
        }