diff --git a/src/include/taler_exchange_service.h b/src/include/taler_exchange_service.h
index caa61c5f1..2dd220293 100644
--- a/src/include/taler_exchange_service.h
+++ b/src/include/taler_exchange_service.h
@@ -1033,6 +1033,85 @@ void
 TALER_EXCHANGE_refund_cancel (struct TALER_EXCHANGE_RefundHandle *refund);
 
 
+/* ********************* POST /csr *********************** */
+
+
+/**
+ * @brief A /csr Handle
+ */
+struct TALER_EXCHANGE_CsRHandle;
+
+
+/**
+ * Details about a response for a CS R request.
+ */
+struct TALER_EXCHANGE_CsRResponse
+{
+  /**
+   * HTTP response data.
+   */
+  struct TALER_EXCHANGE_HttpResponse hr;
+
+  /**
+   * Details about the response.
+   */
+  union
+  {
+    /**
+     * Details if the status is #MHD_HTTP_OK.
+     */
+    struct
+    {
+      /**
+       * Signature over the coin.
+       */
+      struct TALER_DenominationCsPublicR r_pubs;
+    } success;
+
+    /**
+     * Details if the status is #MHD_HTTP_GONE.
+     */
+    struct
+    {
+      /* TODO: returning full details is not implemented */
+    } gone;
+
+  } details;
+};
+
+
+/**
+ * Callbacks of this type are used to serve the result of submitting a
+ * CS R request to a exchange.
+ *
+ * @param cls closure
+ * @param csrr response details
+ */
+typedef void
+(*TALER_EXCHANGE_CsRCallback) (void *cls,
+                               const struct TALER_EXCHANGE_CsRResponse *csrr);
+
+
+/**
+ * Get a CS R using a /csr request.
+ *
+ * @param exchange the exchange handle; the exchange must be ready to operate
+ * @param pk denomination of coin the R's will be used for
+ * @param nonce public nonce for CS R request
+ * @param res_cb the callback to call when the final result for this request is available
+ * @param res_cb_cls closure for the above callback
+ * @return handle for the operation on success, NULL on error, i.e.
+ *         if the inputs are invalid (i.e. denomination key not with this exchange).
+ *         In this case, the callback is not called.
+ */
+struct TALER_EXCHANGE_CsRHandle *
+TALER_EXCHANGE_csr (struct TALER_EXCHANGE_Handle *exchange,
+                    const struct TALER_EXCHANGE_DenomPublicKey *pk,
+                    const struct TALER_WithdrawNonce *nonce,
+                    TALER_EXCHANGE_CsRCallback res_cb,
+                    void *res_cb_cls);
+
+
 /* ********************* GET /reserves/$RESERVE_PUB *********************** */
 
 
diff --git a/src/include/taler_json_lib.h b/src/include/taler_json_lib.h
index 51ebe6d90..d243dd723 100644
--- a/src/include/taler_json_lib.h
+++ b/src/include/taler_json_lib.h
@@ -299,6 +299,18 @@ TALER_JSON_spec_i18n_str (const char *name,
                           const char **strptr);
 
 
+/**
+ * Generate line in parser specification for a CS R.
+ *
+ * @param field name of the field
+ * @param r_pub where the r_pub has to be written
+ * @return corresponding field spec
+ */
+struct GNUNET_JSON_Specification
+TALER_JSON_spec_csr (const char *field,
+                     struct GNUNET_CRYPTO_CsRPublic *r_pub);
+
+
 /**
  * Hash a JSON for binary signing.
  *
diff --git a/src/json/json_helper.c b/src/json/json_helper.c
index 1942d09bd..ef1617ef3 100644
--- a/src/json/json_helper.c
+++ b/src/json/json_helper.c
@@ -658,7 +658,7 @@ TALER_JSON_spec_i18n_str (const char *name,
   return ret;
 }
 
-
+//FIXME:
 enum GNUNET_GenericReturnValue
 TALER_JSON_parse_agemask (const json_t *root,
                           struct TALER_AgeMask *mask)
@@ -688,6 +688,54 @@ TALER_JSON_parse_agemask (const json_t *root,
   }
 
   return GNUNET_OK;
+/**
+ * Parse given JSON object to CS R.
+ *
+ * @param cls closure, NULL
+ * @param root the json object representing data
+ * @param[out] spec where to write the data
+ * @return #GNUNET_OK upon successful parsing; #GNUNET_SYSERR upon error
+ */
+static enum GNUNET_GenericReturnValue
+parse_csr (void *cls,
+           json_t *root,
+           struct GNUNET_JSON_Specification *spec)
+{
+  struct GNUNET_CRYPTO_CsRPublic *r_pub = spec->ptr;
+
+  struct GNUNET_JSON_Specification dspec[] = {
+    GNUNET_JSON_spec_fixed (spec->field, r_pub, sizeof (struct
+                                                        GNUNET_CRYPTO_CsRPublic)),
+    GNUNET_JSON_spec_end ()
+  };
+  const char *emsg;
+  unsigned int eline;
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (root,
+                         dspec,
+                         &emsg,
+                         &eline))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+struct GNUNET_JSON_Specification
+TALER_JSON_spec_csr (const char *field,
+                     struct GNUNET_CRYPTO_CsRPublic *r_pub)
+{
+  struct GNUNET_JSON_Specification ret = {
+    .parser = &parse_csr,
+    .cleaner = NULL,
+    .field = field,
+    .ptr = r_pub
+  };
+
+  return ret;
 }
 
 
diff --git a/src/lib/Makefile.am b/src/lib/Makefile.am
index 3398bdf14..fe2a0b6b1 100644
--- a/src/lib/Makefile.am
+++ b/src/lib/Makefile.am
@@ -24,6 +24,7 @@ libtalerexchange_la_SOURCES = \
   exchange_api_auditor_add_denomination.c \
   exchange_api_curl_defaults.c exchange_api_curl_defaults.h \
   exchange_api_common.c \
+  exchange_api_csr.c \
   exchange_api_handle.c exchange_api_handle.h \
   exchange_api_deposit.c \
   exchange_api_deposits_get.c \
diff --git a/src/lib/exchange_api_csr.c b/src/lib/exchange_api_csr.c
new file mode 100644
index 000000000..fa7010f2c
--- /dev/null
+++ b/src/lib/exchange_api_csr.c
@@ -0,0 +1,307 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2014-2021 Taler Systems SA
+
+  TALER is free software; you can redistribute it and/or modify it under the
+  terms of the GNU General Public License as published by the Free Software
+  Foundation; either version 3, or (at your option) any later version.
+
+  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  TALER; see the file COPYING.  If not, see
+  <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file lib/exchange_api_csr.c
+ * @brief Implementation of /csr requests (get R in exchange used for Clause Schnorr withdraw and refresh)
+ * @author Lucien Heuzeveldt
+ * @author Gian Demarmels
+ */
+#include "platform.h"
+#include <jansson.h>
+#include <microhttpd.h> /* just for HTTP status codes */
+#include <gnunet/gnunet_util_lib.h>
+#include <gnunet/gnunet_json_lib.h>
+#include <gnunet/gnunet_curl_lib.h>
+#include "taler_exchange_service.h"
+#include "taler_json_lib.h"
+#include "exchange_api_handle.h"
+#include "taler_signatures.h"
+#include "exchange_api_curl_defaults.h"
+
+
+/**
+ * @brief A Clause Schnorr R Handle
+ */
+struct TALER_EXCHANGE_CsRHandle
+{
+  /**
+   * The connection to exchange this request handle will use
+   */
+  struct TALER_EXCHANGE_Handle *exchange;
+
+  /**
+   * Function to call with the result.
+   */
+  TALER_EXCHANGE_CsRCallback cb;
+
+  /**
+   * Closure for @a cb.
+   */
+  void *cb_cls;
+
+  /**
+   * Denomination key we are withdrawing.
+   */
+  struct TALER_EXCHANGE_DenomPublicKey pk;
+
+  /**
+   * The url for this request.
+   */
+  char *url;
+
+  /**
+   * Handle for the request.
+   */
+  struct GNUNET_CURL_Job *job;
+
+  /**
+   * Context for #TEH_curl_easy_post(). Keeps the data that must
+   * persist for Curl to make the upload.
+   */
+  struct TALER_CURL_PostContext post_ctx;
+};
+
+
+/**
+ * We got a 200 OK response for the /reserves/$RESERVE_PUB/withdraw operation.
+ * Extract the coin's signature and return it to the caller.  The signature we
+ * get from the exchange is for the blinded value.  Thus, we first must
+ * unblind it and then should verify its validity against our coin's hash.
+ *
+ * If everything checks out, we return the unblinded signature
+ * to the application via the callback.
+ *
+ * @param wh operation handle
+ * @param json reply from the exchange
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR on errors
+ */
+static enum GNUNET_GenericReturnValue
+csr_ok (struct TALER_EXCHANGE_CsRHandle *csrh,
+        const json_t *json,
+        struct TALER_EXCHANGE_CsRResponse *csrr)
+{
+  struct GNUNET_JSON_Specification spec[] = {
+    TALER_JSON_spec_csr ("r_pub_0", &csrr->details.success.r_pubs.r_pub[0]),
+    TALER_JSON_spec_csr ("r_pub_1", &csrr->details.success.r_pubs.r_pub[1]),
+    GNUNET_JSON_spec_end ()
+  };
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (json,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
+  /* r_pubs are valid, return it to the application */
+  csrh->cb (csrh->cb_cls,
+            csrr);
+  /* make sure callback isn't called again after return */
+  csrh->cb = NULL;
+  GNUNET_JSON_parse_free (spec);
+  return GNUNET_OK;
+}
+
+
+/**
+ *
+ * Cancel a CS R request.  This function cannot be used
+ * on a request handle if a response is already served for it.
+ *
+ * @param csrh the withdraw handle
+ */
+void
+TALER_EXCHANGE_csr_cancel (struct TALER_EXCHANGE_CsRHandle *csrh)
+{
+  if (NULL != csrh->job)
+  {
+    GNUNET_CURL_job_cancel (csrh->job);
+    csrh->job = NULL;
+  }
+  GNUNET_free (csrh->url);
+  TALER_curl_easy_post_finished (&csrh->post_ctx);
+  GNUNET_free (csrh);
+}
+
+
+/**
+ * Function called when we're done processing the HTTP /csr request.
+ *
+ * @param cls the `struct TALER_EXCHANGE_CsRHandle`
+ * @param response_code HTTP response code, 0 on error
+ * @param response parsed JSON result, NULL on error
+ */
+static void
+handle_csr_finished (void *cls,
+                     long response_code,
+                     const void *response)
+{
+  struct TALER_EXCHANGE_CsRHandle *csrh = cls;
+  const json_t *j = response;
+  struct TALER_EXCHANGE_HttpResponse hr = {
+    .reply = j,
+    .http_status = (unsigned int) response_code
+  };
+  struct TALER_EXCHANGE_CsRResponse csrr = {
+    .hr = hr
+  };
+
+  csrh->job = NULL;
+  switch (response_code)
+  {
+  case 0:
+    csrr.hr.ec = TALER_EC_GENERIC_INVALID_RESPONSE;
+    break;
+  case MHD_HTTP_OK:
+    if (GNUNET_OK !=
+        csr_ok (csrh,
+                j,
+                &csrr))
+    {
+      GNUNET_break_op (0);
+      csrr.hr.http_status = 0;
+      csrr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+      break;
+    }
+    GNUNET_assert (NULL == csrh->cb);
+    TALER_EXCHANGE_csr_cancel (csrh);
+    return;
+  case MHD_HTTP_BAD_REQUEST:
+    /* This should never happen, either us or the exchange is buggy
+       (or API version conflict); just pass JSON reply to the application */
+    csrr.hr.ec = TALER_JSON_get_error_code (j);
+    csrr.hr.hint = TALER_JSON_get_error_hint (j);
+    break;
+  case MHD_HTTP_NOT_FOUND:
+    /* Nothing really to verify, the exchange basically just says
+       that it doesn't know the /csr.  Can happen if the exchange
+       doesn't support Clause Schnorr.
+       We should simply pass the JSON reply to the application. */
+    csrr.hr.ec = TALER_JSON_get_error_code (j);
+    csrr.hr.hint = TALER_JSON_get_error_hint (j);
+    break;
+  case MHD_HTTP_GONE:
+    /* could happen if denomination was revoked */
+    /* Note: one might want to check /keys for revocation
+       signature here, alas tricky in case our /keys
+       is outdated => left to clients */
+    csrr.hr.ec = TALER_JSON_get_error_code (j);
+    csrr.hr.hint = TALER_JSON_get_error_hint (j);
+    break;
+  case MHD_HTTP_INTERNAL_SERVER_ERROR:
+    /* Server had an internal issue; we should retry, but this API
+       leaves this to the application */
+    csrr.hr.ec = TALER_JSON_get_error_code (j);
+    csrr.hr.hint = TALER_JSON_get_error_hint (j);
+    break;
+  default:
+    /* unexpected response code */
+    GNUNET_break_op (0);
+    csrr.hr.ec = TALER_JSON_get_error_code (j);
+    csrr.hr.hint = TALER_JSON_get_error_hint (j);
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Unexpected response code %u/%d for CS R request\n",
+                (unsigned int) response_code,
+                (int) hr.ec);
+    break;
+  }
+  if (NULL != csrh->cb)
+  {
+    csrh->cb (csrh->cb_cls,
+              &csrr);
+    csrh->cb = NULL;
+  }
+  TALER_EXCHANGE_csr_cancel (csrh);
+}
+
+
+struct TALER_EXCHANGE_CsRHandle *
+TALER_EXCHANGE_csr (struct TALER_EXCHANGE_Handle *exchange,
+                    const struct TALER_EXCHANGE_DenomPublicKey *pk,
+                    const struct TALER_WithdrawNonce *nonce,
+                    TALER_EXCHANGE_CsRCallback res_cb,
+                    void *res_cb_cls)
+{
+  struct TALER_EXCHANGE_CsRHandle *csrh;
+
+  if (TALER_DENOMINATION_CS != pk->key.cipher)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+
+  csrh = GNUNET_new (struct TALER_EXCHANGE_CsRHandle);
+  csrh->exchange = exchange;
+  csrh->cb = res_cb;
+  csrh->cb_cls = res_cb_cls;
+  csrh->pk = *pk;
+
+  {
+    json_t *csr_obj;
+
+    csr_obj = GNUNET_JSON_PACK (GNUNET_JSON_pack_data_varsize ("nonce",
+                                                               nonce,
+                                                               sizeof(struct
+                                                                      TALER_WithdrawNonce)),
+                                GNUNET_JSON_pack_data_varsize ("denom_pub_hash",
+                                                               &pk->h_key,
+                                                               sizeof(struct
+                                                                      TALER_DenominationHash)));
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Attempting to request R with denomination public key %s\n",
+                TALER_B2S (&pk->key.details.cs_public_key));
+    csrh->url = TEAH_path_to_url (exchange,
+                                  "/csr");
+    if (NULL == csrh->url)
+    {
+      json_decref (csr_obj);
+      GNUNET_free (csrh);
+      return NULL;
+    }
+    {
+      CURL *eh;
+      struct GNUNET_CURL_Context *ctx;
+
+      ctx = TEAH_handle_to_context (exchange);
+      eh = TALER_EXCHANGE_curl_easy_get_ (csrh->url);
+      if ( (NULL == eh) ||
+           (GNUNET_OK !=
+            TALER_curl_easy_post (&csrh->post_ctx,
+                                  eh,
+                                  csr_obj)) )
+      {
+        GNUNET_break (0);
+        if (NULL != eh)
+          curl_easy_cleanup (eh);
+        json_decref (csr_obj);
+        GNUNET_free (csrh->url);
+        GNUNET_free (csrh);
+        return NULL;
+      }
+      json_decref (csr_obj);
+      csrh->job = GNUNET_CURL_job_add2 (ctx,
+                                        eh,
+                                        csrh->post_ctx.headers,
+                                        &handle_csr_finished,
+                                        csrh);
+    }
+  }
+
+  return csrh;
+}