Unable to use PLAINTEXT signature with a DotNetOpenAuth ServiceProvider

OAuth Authentication is done in three steps:

1. The Consumer obtains an unauthorized Request Token.

2. The User authorizes the Request Token.

3. The Consumer exchanges the Request Token for an Access Token.

So here's what that would look like:

public class InMemoryTokenManager : IConsumerTokenManager, IOpenIdOAuthTokenManager{private Dictionary<string, string> tokensAndSecrets = new Dictionary<string, string>();public InMemoryTokenManager(string consumerKey, string consumerSecret){    if (String.IsNullOrEmpty(consumerKey))    {        throw new ArgumentNullException("consumerKey");    }    this.ConsumerKey = consumerKey;    this.ConsumerSecret = consumerSecret;}public string ConsumerKey { get; private set; }public string ConsumerSecret { get; private set; }#region ITokenManager Memberspublic string GetConsumerSecret(string consumerKey){    if (consumerKey == this.ConsumerKey)    {        return this.ConsumerSecret;    }    else    {        throw new ArgumentException("Unrecognized consumer key.", "consumerKey");    }}public string GetTokenSecret(string token){    return this.tokensAndSecrets[token];}public void StoreNewRequestToken(UnauthorizedTokenRequest request, ITokenSecretContainingMessage response){    this.tokensAndSecrets[response.Token] = response.TokenSecret;}public void ExpireRequestTokenAndStoreNewAccessToken(string consumerKey, string requestToken, string accessToken, string accessTokenSecret){    this.tokensAndSecrets.Remove(requestToken);    this.tokensAndSecrets[accessToken] = accessTokenSecret;}/// <summary>/// Classifies a token as a request token or an access token./// </summary>/// <param name="token">The token to classify.</param>/// <returns>Request or Access token, or invalid if the token is not recognized.</returns>public TokenType GetTokenType(string token){    throw new NotImplementedException();}#endregion#region IOpenIdOAuthTokenManager Memberspublic void StoreOpenIdAuthorizedRequestToken(string consumerKey, AuthorizationApprovedResponse authorization){    this.tokensAndSecrets[authorization.RequestToken] = string.Empty;}#endregion}

Following block of code may help you to generate plain text signature

public static string GetSignature(OAuthSignatureMethod signatureMethod,             AuthSignatureTreatment signatureTreatment, string signatureBase, string consumerSecret, string tokenSecret){    if (tokenSecret.IsNullOrBlank())    {        tokenSecret = String.Empty;    }    consumerSecret = UrlEncodeRelaxed(consumerSecret);    tokenSecret = UrlEncodeRelaxed(tokenSecret);    string signature;    switch (signatureMethod)    {        case OAuthSignatureMethod.HmacSha1:        {            var crypto = new HMACSHA1();            var key = "{0}&{1}".FormatWith(consumerSecret, tokenSecret);            crypto.Key = _encoding.GetBytes(key);            signature = signatureBase.HashWith(crypto);            break;        }        case OAuthSignatureMethod.PlainText:        {            signature = "{0}&{1}".FormatWith(consumerSecret, tokenSecret);            break;        }        default:            throw new NotImplementedException("Only HMAC-SHA1 is currently supported.");        }        var result = signatureTreatment == OAuthSignatureTreatment.Escaped            ? UrlEncodeRelaxed(signature)            : signature;        return result;    }