blocks|key|1194502|text|显然，在复制原始的base64编码的字符串时，您遗漏了最后两个字符。在输入字符串后加上两个is-equal+(=)符号，它将被正确解码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1194503|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Apparently you missed the last two characters when copying the original base64-encoded string. Suffix the input string with two is-equal (=) signs and it will be decoded correctly.

blocks|key|1194542|text|我在http://sunilarora.org/parsing-signedrequest-parameter-in-python-bas上分享了一个代码片段，用于解析基于python的facebook+canvas应用程序中的signed_request参数|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1194543|import+base64
import+hashlib
import+hmac
import+simplejson+as+json

def+base64_url_decode(inp):
++++padding_factor+=+(4+-+len(inp)+%25+4)+%25+4
++++inp+%2B=+"="*padding_factor+
++++return+base64.b64decode(unicode(inp).translate(dict(zip(map(ord,+u'-_'),+u'%2B/'))))

def+parse_signed_request(signed_request,+secret):

++++l+=+signed_request.split('.',+2)
++++encoded_sig+=+l[0]
++++payload+=+l[1]

++++sig+=+base64_url_decode(encoded_sig)
++++data+=+json.loads(base64_url_decode(payload))

++++if+data.get('algorithm').upper()+!=+'HMAC-SHA256':
++++++++log.error('Unknown+algorithm')
++++++++return+None
++++else:
++++++++expected_sig+=+hmac.new(secret,+msg=payload,+digestmod=hashlib.sha256).digest()

++++if+sig+!=+expected_sig:
++++++++return+None
++++else:
++++++++log.debug('valid+signed+request+received..')
return+data|code-block|syntax|javascript|1194544|entityMap|0|LINK|mutability|MUTABLE|url|http://sunilarora.org/parsing-signedrequest-parameter-in-python-bas^0|2|1V|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

I have shared a code snippet for parsing signed_request parameter in a python based facebook canvas application at <a href="http://sunilarora.org/parsing-signedrequest-parameter-in-python-bas" rel="nofollow noreferrer">http://sunilarora.org/parsing-signedrequest-parameter-in-python-bas</a>:

<pre><code>import base64
import hashlib
import hmac
import simplejson as json

def base64_url_decode(inp):
 padding_factor = (4 - len(inp) % 4) % 4
 inp += "="*padding_factor 
 return base64.b64decode(unicode(inp).translate(dict(zip(map(ord, u'-_'), u'+/'))))

def parse_signed_request(signed_request, secret):

 l = signed_request.split('.', 2)
 encoded_sig = l[0]
 payload = l[1]

 sig = base64_url_decode(encoded_sig)
 data = json.loads(base64_url_decode(payload))

 if data.get('algorithm').upper() != 'HMAC-SHA256':
 log.error('Unknown algorithm')
 return None
 else:
 expected_sig = hmac.new(secret, msg=payload, digestmod=hashlib.sha256).digest()

 if sig != expected_sig:
 return None
 else:
 log.debug('valid signed request received..')
return data
</code></pre>

blocks|key|980236|text|import+base64
import+simplejson+as+json

def+parse_signed_request(+signed_request+):
++++encoded_sig,+payload+=+signed_request.split('.',2)
++++data+=+json.loads(base64.b64decode(+payload.replace('-_',+'%2B/')+))
++++return+data|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|980237|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>import base64
import simplejson as json

def parse_signed_request( signed_request ):
 encoded_sig, payload = signed_request.split('.',2)
 data = json.loads(base64.b64decode( payload.replace('-_', '+/') ))
 return data
</code></pre>

blocks|key|1194604|text|试一试|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1194605|s+=+'iEPX-SQWIR3p67lj_0zigSWTKHg'
base64.urlsafe_b64decode(s+%2B+'='+*+(4+-+len(s)+%25+4))|code-block|syntax|javascript|1194606|因为它被写成here|offset|length|1194607|entityMap|0|LINK|mutability|MUTABLE|url|http://fi.am/entry/urlsafe-base64-encodingdecoding-in-two-lines/^0|0|0|6|4|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

try

<pre><code>s = 'iEPX-SQWIR3p67lj_0zigSWTKHg'
base64.urlsafe_b64decode(s + '=' * (4 - len(s) % 4))
</code></pre>


as it is written <a href="http://fi.am/entry/urlsafe-base64-encodingdecoding-in-two-lines/" rel="noreferrer">here</a>

blocks|key|980347|text|作为@dae.eklen解决方案的替代方案，您可以在其后面附加===：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|980348|s+=+'iEPX-SQWIR3p67lj_0zigSWTKHg'
base64.urlsafe_b64decode(s+%2B+'===')|code-block|syntax|javascript|980349|这之所以有效，是因为Python只会抱怨缺少填充，而不是额外的填充。|980350|entityMap^0|V|3|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

Alternative to @dae.eklen's solution, you can append <code>===</code> to it:

<pre><code>s = 'iEPX-SQWIR3p67lj_0zigSWTKHg'
base64.urlsafe_b64decode(s + '===')
</code></pre>

This works because Python only complains about missing padding, but not extra padding.

blocks|key|1194744|text|令人惊讶，但目前接受的答案并不完全正确。正如其他一些答案所述，它是一种称为base64url编码的东西，是RFC7515的一部分。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1194745|基本上，它们将'%2B‘和'/’字符分别替换为'-‘和'_’；此外，还删除了任何尾随的'=‘字符，因为只需查看编码的字符串长度，就可以知道丢失了多少字符。|1194746|下面是C#中的RFC7515示例：|1194747|+static+string+base64urlencode(byte+[]+arg)
+{
+++string+s+=+Convert.ToBase64String(arg);+//+Regular+base64+encoder
+++s+=+s.Split('=')[0];+//+Remove+any+trailing+'='s
+++s+=+s.Replace('%2B',+'-');+//+62nd+char+of+encoding
+++s+=+s.Replace('/',+'_');+//+63rd+char+of+encoding
+++return+s;
+}

+static+byte+[]+base64urldecode(string+arg)
+{
+++string+s+=+arg;
+++s+=+s.Replace('-',+'%2B');+//+62nd+char+of+encoding
+++s+=+s.Replace('_',+'/');+//+63rd+char+of+encoding
+++switch+(s.Length+%25+4)+//+Pad+with+trailing+'='s
+++{
+++++case+0:+break;+//+No+pad+chars+in+this+case
+++++case+2:+s+%2B=+"==";+break;+//+Two+pad+chars
+++++case+3:+s+%2B=+"=";+break;+//+One+pad+char
+++++default:+throw+new+System.Exception(
+++++++"Illegal+base64url+string!");
+++}
+++return+Convert.FromBase64String(s);+//+Standard+base64+decoder
+}|code-block|syntax|javascript|1194748|entityMap|0|LINK|mutability|MUTABLE|url|https://www.rfc-editor.org/rfc/rfc7515#appendix-C^0|1H|7|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|C|$K|L]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

Surprising, but currently accepted answer is not exactly correct.
Like some other answers stated, it's something called base64url encoding, and it's a part of <a href="https://www.rfc-editor.org/rfc/rfc7515#appendix-C" rel="nofollow noreferrer">RFC7515</a>.
Basically, they replaced '+' and '/' chars by '-' and '_' respectively; and additionally removed any trailing '=' chars, because you can always tell how many chars you're missing, just by looking at the encoded string length.
Here's illustrative example from RFC7515 in C#:
<pre><code> static string base64urlencode(byte [] arg)
 {
 string s = Convert.ToBase64String(arg); // Regular base64 encoder
 s = s.Split('=')[0]; // Remove any trailing '='s
 s = s.Replace('+', '-'); // 62nd char of encoding
 s = s.Replace('/', '_'); // 63rd char of encoding
 return s;
 }

 static byte [] base64urldecode(string arg)
 {
 string s = arg;
 s = s.Replace('-', '+'); // 62nd char of encoding
 s = s.Replace('_', '/'); // 63rd char of encoding
 switch (s.Length % 4) // Pad with trailing '='s
 {
 case 0: break; // No pad chars in this case
 case 2: s += &quot;==&quot;; break; // Two pad chars
 case 3: s += &quot;=&quot;; break; // One pad char
 default: throw new System.Exception(
 &quot;Illegal base64url string!&quot;);
 }
 return Convert.FromBase64String(s); // Standard base64 decoder
 }
</code></pre>

blocks|key|980510|text|这是正确的解决方案。在python中有base64.b64encode，但只有base64编码，它与base64+url编码不同。下面是将form+base64encoded转换为base64urlencoded字符串的正确步骤：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|980511|从生成的字符串中，将"/“替换为"_”，将"%2B“替换为”-“去掉尾随的"==”。|980512|等着瞧！这将使其成为base64+url解码的有效字符串。顺便说一句，@dae.eklen上面答案中的链接现在已经断了。|980513|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

This is the right solution. In python there is base64.b64encode but that only base64 encodes and its is different from base64 url encoding. Here is the right set to of steps to convert form base64encoded to base64urlencoded string: 
1. From the resultant string, replace "/" with "_" and "+" with "-" 
2. Strip the trailing "==". 

Et voila! That will make it a valid string for base64 url decoding. Btw, that link in @dae.eklen 's answer above is broken now.

blocks|key|980572|text|如果您从.net发送base64字符串作为参数，似乎在URI，即%2B或/中具有特殊含义的字符被"+"空格替换。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|980573|因此，在用.net发送字符串之前，您可能应该这样做|980574|base64img.Replace("%2B",+"-").Replace("/",+"_"))|code-block|syntax|javascript|980575|然后在python中解码字符串(也添加'=‘，直到长度可以被4整除)|980576|def+decode_base64(data):
++++data+%2B=+'='+*+(len(data)+%25+4)
++++return+base64.urlsafe_b64decode(data)|980577|此外，如果您想在openCV中使用该图像|980578|def+get_cv2_img_from_base64(base_64_string):
++++data+=+decode_base64(base_64_string)
++++np_data+=+np.frombuffer(data,+dtype=np.uint8)
++++return+cv2.imdecode(np_data,+cv2.IMREAD_UNCHANGED)|980579|entityMap^0|4|4|A|6|W|1|Y|1|1A|3|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|17|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|19|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1B|8|@]|D|@]|E|$]]|$1|S|3|T|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|U|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|V|$]]

If you are sending your <code>base64</code> string from <code>.net</code> as a param it seems that chars that have special meaning in the URI ie <code>+</code> or <code>/</code> are replaced with <code>" "</code> spaces.

So before you send your string in .net you should probably do something like this

<pre><code>base64img.Replace("+", "-").Replace("/", "_"))
</code></pre>

Then in python decode the string (also add '=' until the length is divisible by 4)

<pre><code>def decode_base64(data):
 data += '=' * (len(data) % 4)
 return base64.urlsafe_b64decode(data)
</code></pre>

Further if you want to use the image in openCV

<pre><code>def get_cv2_img_from_base64(base_64_string):
 data = decode_base64(base_64_string)
 np_data = np.frombuffer(data, dtype=np.uint8)
 return cv2.imdecode(np_data, cv2.IMREAD_UNCHANGED)
</code></pre>

blocks|key|1194881|text|只是|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1194882|base64.urlsafe_b64decode(s)|code-block|syntax|javascript|1194883|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

just
<pre><code>base64.urlsafe_b64decode(s)
</code></pre>

For Facebook fbml Apps Facebook is sending in a signed_request parameter explained here:

<a href="http://developers.facebook.com/docs/authentication/canvas" rel="noreferrer">http://developers.facebook.com/docs/authentication/canvas</a>

They have given the php version of decoding this signed request:

<a href="http://pastie.org/1054154" rel="noreferrer">http://pastie.org/1054154</a>

How to do the same in python?

I tried base64 module but I am getting Incorrect padding error:

<pre><code>&gt;&gt;&gt; base64.urlsafe_b64decode("eyJhbGdvcml0aG0iOiJITUFDLVNIQTI1NiIsImV4cGlyZXMiOjEyNzk3NDYwMDAsIm9hdXRoX3Rva2VuIjoiMjk1NjY2Njk1MDY0fDIuRXpwem5IRVhZWkJVZmhGQ2l4ZzYzUV9fLjM2MDAuMTI3OTc0NjAwMC0xMDAwMDA0ODMyNzI5MjN8LXJ6U1pnRVBJTktaYnJnX1VNUUNhRzlNdEY4LiIsInVzZXJfaWQiOiIxMDAwMDA0ODMyNzI5MjMifQ")
Traceback (most recent call last):
 File "&lt;stdin&gt;", line 1, in &lt;module&gt;
 File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/base64.py", line 112, in urlsafe_b64decode
 return b64decode(s, '-_')
 File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/base64.py", line 76, in b64decode
 raise TypeError(msg)
TypeError: Incorrect padding
</code></pre>

How to decode base64 url in python?

Python

对于Facebook的fbml应用程序，Facebook正在发送一个signed_request参数，如下所示：他们给出了解码这个签名请求的php版本：如何在python中做同样的事情呢？我尝试了base64模块，但是我得到了错误的填充错误：>>> base64.urlsafe_b64decode("eyJhbGdvc...

问如何在python中解码base64 url？
EN

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问如何在python中解码base64 url？
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